support msgpack 1.2.2 (1.4-maint)

[ThomasWaldmann]

Allow the msgpack 1.2.2 release: bump the upper bound in pyproject.toml and in is_supported_msgpack().

No changelog entry, as 1.4-maint currently has no "not released yet" section.

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

Master: #10218

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.15%. Comparing base (92c7f07) to head (9833344).
⚠️ Report is 1 commits behind head on 1.4-maint.

Additional details and impacted files

@@            Coverage Diff             @@
##           1.4-maint   #10219   +/-   ##
==========================================
  Coverage      82.14%   82.15%           
==========================================
  Files             38       38           
  Lines          11475    11475           
  Branches        1807     1807           
==========================================
+ Hits            9426     9427    +1     
+ Misses          1464     1463    -1     
  Partials         585      585           

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