Refactor _tool.py into separate modules

[nathanjmcdougall]

No description provided.

[codspeed-hq]

CodSpeed Performance Report

Merging #573 will not alter performance

_{Comparing 568-split-usethis_tool-into-modules (788150b) with main (9db5443)}

Summary

✅ 1 untouched benchmarks

[codecov]

Codecov Report

Attention: Patch coverage is 97.25434% with 19 lines in your changes missing coverage. Please review.

Project coverage is 97.38%. Comparing base (c919768) to head (788150b).
Report is 2 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/usethis/_tool/impl/pytest.py	91.20%	8 Missing ⚠️
src/usethis/_tool/impl/ruff.py	96.94%	4 Missing ⚠️
src/usethis/_tool/impl/coverage.py	94.59%	2 Missing ⚠️
src/usethis/_tool/impl/deptry.py	96.77%	2 Missing ⚠️
src/usethis/_tool/config.py	97.36%	1 Missing ⚠️
src/usethis/_tool/impl/import_linter.py	99.07%	1 Missing ⚠️
src/usethis/_tool/impl/requirements_txt.py	96.15%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #573      +/-   ##
==========================================
+ Coverage   97.27%   97.38%   +0.10%     
==========================================
  Files          87      100      +13     
  Lines        4152     4325     +173     
==========================================
+ Hits         4039     4212     +173     
  Misses        113      113              

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