Run focused tests for changed Python files

[forest-savage1234]

Summary

• Map changed source modules for the detected project to their corresponding unittest modules and run changed tests directly.
• Run the full suite for configuration, shared, or unmapped Python changes; skip Python tests for documentation-only diffs.
• Make --all-files select the full suite for tests as well as linting.
• Pass subprocess arguments as a list without invoking a shell, and resolve candidate tests relative to --project-path.

Closes #1019

Validation

• ReviewHelperTest — 2 test methods passed, covering the native l2tdevtools mapping, a cross-project dfvfs mapping, documentation-only changes, configuration changes, and --all-files.
• Black left all three touched files unchanged.
• git diff --check.

Scope notes

Unknown or shared Python changes deliberately fall back to the full suite rather than risking an incomplete focused run. The source-prefix mapping uses the project name detected by ProjectHelper, so the helper remains usable across the supported log2timeline/ForensicArtifacts repositories.