Switch the build backend from poetry-core to maturin

[anoadragon453]

This PR switches the build backend from poetry-core to maturin. This was prompted by the switch to poetry 2.x in #19137 being incompatible with Linux distributions that still only ship poetry 1.x. maturin should be supported on said distributions.

maturin it comes with the benefit of better PyO3 support. For instance, we can now remove the .ci/scripts/auditwheel_wrapper.py script which was needed to make the wheels produced by poetry-core include abi3 in the tags, instead of cpX.

Importantly, poetry install ... will still work and still build the synapse rust module. Development workflows do not need to change.

I've held off on migrating the [tool.poetry.group.dev.dependencies] section to [dependency-groups].dev (which was deliberately excluded in #19137). These dependencies are only for development of Synapse (running the release script, checking types, etc.). Switching to [dependency-groups] section would end up requiring poetry 2.2.0+ (and pip 25.1+). Despite this, as of #19137, pip install .[all] will install all other dependencies, which is enough to build packages.

You can then use maturin build (or cibuildwheel, as we do) to build packaged wheels under target/wheels/; no need for poetry nor poetry-core 2.x to be directly involved in the build process.

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maturin includes its own auditwheel implementation. cibuildwheel will by default run auditwheel repair when building on Linux. In the interest of not breaking our wheels, we've opted to leave both implementations in place. We can look into disabling one of them separately.

Dev notes

Discussed in the internal backend team lobby room

Pull Request Checklist

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