fix: fix frame_metadata and various metadata typing

[tlambert03]

there was a bug in ND2File.frame_metadata

[codecov]

Codecov Report

Merging #155 (229fb29) into main (52e5e01) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #155      +/-   ##
==========================================
+ Coverage   93.18%   93.28%   +0.10%     
==========================================
  Files          15       15              
  Lines        2229     2220       -9     
==========================================
- Hits         2077     2071       -6     
+ Misses        152      149       -3     

Impacted Files	Coverage Δ
src/nd2/_pysdk/_sdk_types.py	100.00% <ø> (ø)
src/nd2/_pysdk/_parse.py	93.48% <100.00%> (+0.49%)	⬆️
src/nd2/_pysdk/_pysdk.py	91.44% <100.00%> (+0.37%)	⬆️
src/nd2/structures.py	96.07% <100.00%> (-0.03%)	⬇️

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[codspeed-hq]

CodSpeed Performance Report

Merging #155 will degrade performances by 53.41%

_{Comparing fix-frame-meta (229fb29) with main (52e5e01)}

🎉 Hooray! pytest-codspeed just leveled up to 2.0.0!

A heads-up, this is a breaking change and it might affect your current performance baseline a bit. But here's the exciting part - it's packed with new, cool features and promises improved result stability 🥳!
Curious about what's new? Visit our releases page to delve into all the awesome details about this new version.

Summary

❌ 1 regressions
✅ 12 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	fix-frame-meta	Change
❌	test_time_imread_dask[jonas_control002]	1.6 s	3.5 s	-53.41%