Fix added_lines and deleted_lines dropping "++" and "--" content - #324

ModifiedFile.added_lines skips every diff line starting with +++, and ModifiedFile.deleted_lines skips every one starting with ---, to avoid counting the +++ b/file and --- a/file patch headers. Those headers are never in the string being scanned: GitPython's Diff.re_header matches them as part of the header block and assigns Diff.diff only the text that follows, so ModifiedFile.diff always starts at the first @@. The guards can therefore only match real content. An added line ++i; appears as +++i; in the patch and a deleted line --i; appears as ---i;, and both go uncounted.

So the counts disagree with Commit.insertions and Commit.deletions, which come from numstat, and with ModifiedFile.diff_parsed, which classifies the same lines with no header guard, as does HunksCount at pydriller/metrics/process/hunks_count.py:45. There is already a case in the bundled repos: in test-repos/diff, commit 156111a7 deletes 9 lines from docs/reference.rst, one of them the reST underline ----------------, and deleted_lines returns 8 while git diff --numstat and diff_parsed["deleted"] both say 9. Everything built on these two properties inherits the undercount, including CodeChurn, LinesCount, ContributorsCount, ContributorsExperience and HistoryComplexity.

The fix drops both guards in pydriller/domain/commit.py, so every + and - line in the hunk body is counted.

Two tests in tests/test_commit.py: one over test-repos/diff that pins the reference.rst count at 9 and checks the per-file sums now match Commit.insertions and Commit.deletions, and one that runs a small patch containing +++i; and ---i; through a mocked Diff. On master they fail with assert 8 == 9 and assert 0 == 1. With the change, mypy --ignore-missing-imports pydriller/ tests/, flake8 and pytest tests/ all pass locally on Python 3.11 on macOS.