cabal 3.18.1.0 effectively dropped semaphore support

cabal 3.18.1.0 effectively dropped semaphore support because no released GHC version supports v2, which is, well, disappointing.

I'm not sure why compat support for v1 was not included. At first I thought it was deemed too expensive or problematic, but I now have a Claude-generated [support for both v1 and v2](https://github.com/arybczak/cabal/commit/202526d3c6b5572fc5904efb787f0755caef7625) that isn't particularly complicated and seems to work just fine.

If anyone cares enough to take care of this, feel free to take the commit.

Start by reviewing the linked commit and the existing semaphore support in Cabal to understand how GHC versions select semaphore compatibility. The work is done when released GHC versions without v2 support retain working v1 support while v2 support continues to work.

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