Add RWLock and ManagedAsynchronousAccess

[Supereg]

Add RWLock and ManagedAsynchronousAccess

♻️ Current situation & Problem

This PR adds the RWLock, RecursiveRWLock and ManagedAsynchronousAccess infrastructure that was previously introduced in SpeziBluetooth (see StanfordSpezi/SpeziBluetooth#45 and StanfordSpezi/SpeziBluetooth#47).
This changes require the Swift 6 toolchain. Therefore, we increase the required swift tools version to 6.0.

This PR introduces the final changes for the SpeziFoundation 2.0 release (assuming #16 is merged beforehand).

⚙️ Release Notes

• Added RWLock and RecursiveRWLock
• Added ManagedAsynchronousAccess
• Only require sending closure with withTimeout instead of a @Sendable one.

📚 Documentation

Updated the documentation catalog, adding a new "Concurrency" topics section.

✅ Testing

Added unit test for the new components.

📝 Code of Conduct & Contributing Guidelines

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• I agree to follow the Code of Conduct and Contributing Guidelines.

[Supereg]

@PSchmiedmayer The CI is currently failing as we are still using Xcode 15 as the stable release. I would avoid setting all the GitHub jobs to use the latest version of Xcode. Otherwise, we would need to change everything back.
I assume the Xcode would be release next Monday alongside the OS releases. I would wait till we upgraded the runner to use Xcode 16 by default to merge the PR if that makes sense 👍

[codecov]

Codecov Report

Attention: Patch coverage is 97.91667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 91.27%. Comparing base (17bd0e0) to head (69c7af7).

Files with missing lines	Patch %	Lines
Sources/SpeziFoundation/Concurrency/RWLock.swift	93.23%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #17      +/-   ##
==========================================
+ Coverage   83.06%   91.27%   +8.21%     
==========================================
  Files           9       12       +3     
  Lines         301      492     +191     
==========================================
+ Hits          250      449     +199     
+ Misses         51       43       -8     

Files with missing lines	Coverage Δ
...s/SpeziFoundation/Concurrency/AsyncSemaphore.swift	80.30% <ø> (ø)
...dation/Concurrency/ManagedAsynchronousAccess.swift	100.00% <100.00%> (ø)
.../SpeziFoundation/Concurrency/RecursiveRWLock.swift	100.00% <100.00%> (ø)
Sources/SpeziFoundation/Misc/TimeoutError.swift	60.00% <100.00%> (ø)
Sources/SpeziFoundation/Concurrency/RWLock.swift	93.23% <93.23%> (ø)

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