Bump pytest-codspeed to v2.1.0

[art049]

Change Summary

Bumps pytest-codspeed to the latest version.
Also moves the dependency to tests/requirements.txt so that the Python cache works appropriately when pytest-codspeed is bumped.

There is still an incompatibility issue with pytest-speed that requires it to be uninstalled so that pytest-codspeed can work properly in the action as described in CodSpeedHQ/pytest-codspeed#16. However, installing pytest-benchmark is no longer required to have pytest-codspeed working but I think it's required to generate the PGO data in your workflow.
Normally, using outside the action pytest tests/benchmarks --codspeed can run the benchmarks (without pytest-speed nor pytest-benchmark).

[codecov]

Codecov Report

Merging #875 (d9b1a13) into main (040985f) will increase coverage by 0.00%.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #875   +/-   ##
=======================================
  Coverage   93.82%   93.83%           
=======================================
  Files         104      104           
  Lines       15365    15365           
  Branches       25       25           
=======================================
+ Hits        14416    14417    +1     
+ Misses        943      942    -1     
  Partials        6        6           

see 1 file with indirect coverage changes

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[codspeed-hq]

CodSpeed Performance Report

Merging #875 will degrade performances by 52.74%

_{Comparing art049:bump-pytest-codspeed-v2-1-0 (d9b1a13) with main (040985f)}

🎉 Hooray! pytest-codspeed just leveled up to 2.1.0!

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

❌ 2 regressions
✅ 136 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	main	art049:bump-pytest-codspeed-v2-1-0	Change
❌	test_tagged_union_int_keys_python	33.2 µs	63.4 µs	-47.61%
❌	test_decimal_from_string_core	32.9 µs	69.5 µs	-52.74%

[davidhewitt]

Many thanks, this looks promising to me, we'll give it a shot and see what happens!