rust-cpython: also accept the `filteredrevs` argument in index.headrevs The C version have been accepting this argument since Mercurial 3.2, lets align the Rust index here. This will make it possible to simplify the code in later changesets.

branchmap: use the proper experimental name in cacheutil Otherwise they are not properly copied around.

interfaces: introduce and use a protocol class for the `mpatch` module See f2832de2a46c for details when this was done for the `bdiff` module. Two things worth pointing out- 1) The `cffi` module "inherits" the `pure` implementation of `patchedsize()` because of its wildcard import. 2) It's odd that the `mpatchError` lives in both `pure` and `cext` modules. I initially thought to move the exception into the new class, and make the existing class name an alias to the class in the new location, but the exception is created in C code by the `cext` module, so that won't work. I don't think a protocol class is approriate, because there's nothing special about the class to distinguish from any other `Exception`. Fortunately, nobody is catching this exception in core, so we can kick the can down the road.

branching: merge stable into default

doctest: use the system hg to find the list of file to tests Same as what we do for the `.t` tests, but more manually.

relnotes: skip the test if the source repository is not readable The test want to run the relnot extension, with the tested mercurial, on the original repository. This is not always possible (e.g. when running with --pure and the repository use zstd for example). So we skip the test in this case.

check-code: document reason and suggest alternative to exit code negation The check was introduced in f48b075ff088. We trust the explanation from there.

ci: drop the HGMODULEPOLICY overwrite The test runner have been setting them properly for a while now. So we don't need to do it manually anymore.

test: preserve the existing module policy config for testrepohg resuse The test runner is, righfully, setting HGMODULEPOLICY to match the flavor requests to run the tests. However this mess with the `testrepohg` ability to run properly, as the newly set policy might be incompatible with its installation, or its ability to read the test repo. So we preserve the initial value in a dedicated variable and use it in the `testrepohg` helper.

module-policy: ignore empty module policy This make the variable easier to work with, the empty value is not ambiguous about not wanting to get in the way.