pytest fixtures: hg / git configurations to session scope

[tony]

Resolves #474

Problem

Issue #472 requires session-scoped fixtures.

Currently, we use set_home, gitconfig, and hgconfig to monkeypatch.setenv $HOME, pointing it to a temporary directory with user-specific configuration files. This ensures all subsequent git and hg commands automatically load these configurations.

However, monkeypatch.setenv doesn't work with function-scoped fixtures.

Improvement

❯ hyperfine \
  --warmup 3 \
  --runs 10 \
  --prepare 'git checkout master' \
  --command-name 'libvcs 0.31.0' \
  'py.test' \
  --prepare 'git checkout pytest-config' \
  --command-name 'with improved hg/git config fixtures' \
  'py.test'
Benchmark 1: libvcs 0.31.0
  Time (mean ± σ):     15.150 s ±  0.751 s    [User: 16.650 s, System: 4.720 s]
  Range (min … max):   14.235 s … 16.741 s    10 runs

Benchmark 2: with improved hg/git config fixtures
  Time (mean ± σ):     15.014 s ±  0.307 s    [User: 17.246 s, System: 4.865 s]
  Range (min … max):   14.458 s … 15.642 s    10 runs

Summary
  with improved hg/git config fixtures ran
    1.01 ± 0.05 times faster than libvcs 0.31.0

Changes

pytest fixtures: Session-scoped hgconfig and gitconfig

These are now set by set_hgconfig and set_gitconfig, which set HGRCPATH and GIT_CONFIG, instead of overriding HOME.

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 2 lines in your changes missing coverage. Please review.

Project coverage is 64.52%. Comparing base (58a9247) to head (43eebcb).
Report is 11 commits behind head on master.

Files with missing lines	Patch %	Lines
src/libvcs/pytest_plugin.py	88.23%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #475      +/-   ##
==========================================
+ Coverage   64.17%   64.52%   +0.34%     
==========================================
  Files          40       40              
  Lines        3713     3721       +8     
  Branches      788      789       +1     
==========================================
+ Hits         2383     2401      +18     
+ Misses        793      782      -11     
- Partials      537      538       +1     

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