support msgpack 1.2.2

[ThomasWaldmann]

Allow the msgpack 1.2.2 release: bump the upper bound in pyproject.toml and in is_supported_msgpack(), plus a changelog entry.

The 1.2.1 -> 1.2.2 diff contains only fixes, nothing that affects how borg uses msgpack:

• Timestamp.from_datetime now uses integer timedelta arithmetic instead of the float datetime.timestamp() (which was off by one second far from the epoch and raised OverflowError near datetime.max)
• out-of-range timestamp nanoseconds are rejected in all timestamp= modes
• ExtraData.extra is copied out of the temporary contiguous buffer before that buffer is released (non-contiguous memoryview input)
• PyFloat_Pack4 return value is checked in msgpack_pack_float
• new RuntimeError guard against re-entrant Unpacker.feed() from a hook - borg never feeds from inside a hook
• fallback Unpacker.skip() translates RecursionError into StackError

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.29%. Comparing base (2491d56) to head (0ad66ed).
⚠️ Report is 38 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10218      +/-   ##
==========================================
+ Coverage   87.20%   87.29%   +0.08%     
==========================================
  Files         102      102              
  Lines       18394    18444      +50     
  Branches     2829     2834       +5     
==========================================
+ Hits        16040    16100      +60     
+ Misses       1644     1638       -6     
+ Partials      710      706       -4     

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