fix(tsa)!: parse optional RFC 3161 status text

[wolfv]

Summary

• Add optional statusString between status and failInfo in PkiStatusInfo.
• Preserve rejection handling and validate UTF-8 through the existing DER decoder.

Regression covers full timestamp verification, Unicode, optional-field ordering, rejected responses, and malformed strings.

Compatibility: public PkiStatusInfo struct literals must now specify status_string (typically None).

Stack

Fix 2/6 from the crate review. Based on #214; merge the stack in order. This PR contains only its focused fix relative to its base.

Validation

• Targeted regression tests pass.
• cargo test --workspace --all-features --locked passes on the completed stack.
• Strict Clippy (--all-targets --all-features --locked -- -D warnings) passes for the changed crates.
• cargo fmt --all -- --check and git diff --check pass.