chore(help-md-gen): address roborev #2146 review findings

[jqnatividad]

Summary

Three LOW-severity follow-ups to #3858 from roborev job 2146:

• Drop boolean from classify_rust_type and extract_arg_types_from_source docstrings — the function never returns boolean (bool maps to flag), so the docs were out of sync with the implementation.
• Replace the substring-based struct Args lookup with a regex ((?m)^\s*(?:pub(?:\([^)]*\))?\s+)?struct\s+Args\b) so future generic-parameter or no-space-before-brace shapes (struct Args<'a>, struct Args<T>, struct Args{) keep working. Word-boundary anchored to avoid matching ArgsExtra.
• Document the single-line type-capture limitation in the function docstring — a future flag_x:\n Option<…>, field would silently fall back to string.

No behavior change for any current command: qsv --generate-help-md produces byte-identical output.

Test plan

• cargo build --locked --bin qsv -F all_features
• cargo clippy --bin qsv -F all_features -- -D warnings
• cargo test --bin qsv -F all_features help_markdown_gen — 25/25 pass (new test: test_extract_arg_types_handles_generic_args_and_no_space_before_brace covers Args<'a>, Args<T>, and Args{)
• cargo +nightly fmt
• ./target/debug/qsv --generate-help-md — clean working tree (no doc changes vs master)

🤖 Generated with Claude Code

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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[Copilot]

Pull request overview

This PR is a small follow-up to the help-markdown generator improvements, keeping documentation accurate and making the Args-struct discovery logic more robust to future Rust syntax shapes (generics and brace spacing) without changing current generated output.

Changes:

• Align docstrings with actual behavior by removing the nonexistent boolean display type and clarifying that bool maps to flag.
• Replace substring-based struct Args detection with a regex-based match that tolerates pub(...), generics (e.g. Args<'a>, Args<T>), and struct Args{ formatting.
• Add test coverage for the new Args-struct matching shapes and document the single-line type-capture limitation.