For each origin it calls an http api endpoint to retrieve extrinsic
metadata for each version of a module.
Author and package description are extracted from intrinsic metadata
parsing data from META.json or META.yml at the root of the archive.

Related T2833

Software Heritage homemade RPC layer does not known how to serialize
set objects so we need to pass lists as parameters of *_missing
methods from storage API.

This will allow us to use this interface in async code like ``swh-scanner``.

Unfortunately, this means calling ``asyncio.run`` for sync code, but the
performance impact should be negligible.

The ``swh_storage.*missing*`` APIs are inconsistent for each type, which
requires a lot of boilerplate code. This should be addressed in a
follow-up.

"Discovery" is the term used to find out the differences between two
Merkle graphs. Using such an algorithm is useful in that it drastically
reduces the amount of data that needs to be transferred.

This commit introduces an efficient but simple algorithm that is a good
starting point for improved performance: random sampling of directories,
the details of which are explained in the docstrings.

Mercurial uses a more sophisticated algorithm for its discovery, but it
is quite a bit more involved and would introduce too much complexity at
once. Also, the constraints for speed that Mercurial has (in the order
of milliseconds) don't apply as obviously to this context without
further investigation.

Benchmarks
==========

Setup
-----
- With a local postgresql storage (so no network overhead), a local
  tmpfs obstorage on a fast NVME SSD, all of which should make this
  improvement look less good than it will be in production
- With a tarball of the linux kernel at commit
  d96d875ef5dd372f533059a44f98e92de9cf0d42 already loaded
- Loading a tarball of 20 commits earlier
  (bf3f401db6cbe010095fe3d1e233a5fde54e8b78)
- Only taking into account the loading (not the downloading of the
  tarball, or its decompression)

Result
------

before: ~30s
after: ~17s

Reproduced 4 times.

This naming is more explicit about what this function is doing.

This function is used in multiple package loaders so add a throttling
retry policy and debug log about fetched URL.

Some package loaders might encounter errors while attempting to get
package info for a given version (HTTP error for instance).

So handle that case and ensure partial visit when such an error occurs.

Related to T4124

Those methods were not reimplemented and could return incorrect statuses
once the load method called.

As they are useful for tests, implement them in PackageLoader class.

Such test was missing so add a couple of tiny tarballs in tests
data directory and simulate a successful visit for origin example.

Also update origin URL and remove a couple of hardcoded litterals.

Some go packages only have a development version not listed by the
@v/list endpoint but returned by the @latest endpoint.

So ensure to return it in get_versions method or it will be missed
by the loader.

Related to T4124

When a go package name contains uppercase characters in it, associated
goproxy URLs need to be case-encoded by replacing every uppercase letter
with an exclamation mark followed by the corresponding lower-case letter.

This fixes the loading of such packages.

See https://go.dev/ref/mod#goproxy-protocol.

Related to T4124

Make use of packaging.versions instead of distutils versions classes
that are deprecated

Resolves T4528
Related T4465

It enables to search sentry events related to a particular loaded origin
URL or for a given visit type from the sentry Web UI.

Origin URL for a package listed by the pubdev lister is now in the form
https://pub.dev/packages/<package_name> so we need to reconstruct the
API URL to get package versions from it.

Some HTTP download requests might be throttled by remote servers
so add retry mechanism with exponential backoff to fix tarball
downloads in some loaders.

This uses the Golang proxy since that's what `go get` uses, and since it
probably offer better performance than most direct sources.

Fix an issue where get_versions failed when version names does not
follow semver conventions.
Add related test.

The method name was wrong replace it with 'load_pubdev'

Call an http api endpoint per package to get all its versions and
artifacts metadata.

Adapt code, test fixture and tests after the lister split its artifacts
data to artifacts and arch_metadata (see D8259)

Related T4233

Add 'aur' package loader

It seems that despite setting it in the 'except BaseException' block,
it is still occasionally undefined in the 'finally' block when
triggered by a SystemExit exception.

This should hopefully prevent UnboundLocalError from
being raised from the 'finally' block from now on

This fix an issue discovered while testing loader on docker environment,
error was (load_arch() got an unexpected keyword argument
'lister_name')

Related T4233

named args

This fix an issue discovered while testing loader on docker environment,
error was (load_crates() got an unexpected keyword argument 'lister_name')

Related T4104

They should use the same convention as Git.

Fetch Arch linux packages from lister discovered origins.
For each origin it get versions from extra_loader_arguments['artifacts']

Arch Linux package can comes as .xz or .zst file archive.
Support for .zst (Zstandard compression) has been requested with D7993.

Related to T4233

An artifact without time info can be provided in the artifacts list
parameter of the loader (for instance last modification date
is not available for tarballs coming from github releases).

That case was not handled by the archive loader wich was resulting
in loading error so add fix for it.

It will be used by the git loader to run a graph traversal on
received packfiles; and we want to monitor its runtime as a separate
metric.

It will be used by the git loader to compute metrics on the number
of objects ignored by the filtering proxy

The post_load method of a loader can raise an exception so we must
ensure to turn back the success variable to False in that case.

For instance, the subversion loader post_load checks that latest
exported revision is consistent with what the official subversion
client produces. If it is not an exception will be raised to set
the visit status to partial.

Related to T4236