chore: improve clap maintenance path

[vip892766gma]

Summary:

• Add focused unit tests for edge cases in str_to_bool (whitespace, mixed case, empty string, unicode lookalikes) and for suggestions::did_you_mean (empty candidate list, identical strings, very long inputs, non-ASCII) to lock down current behavior and improve branch coverage in these small utility modules.
• Keep the change narrow so it is straightforward to review.

Notes:

• I kept this scoped to the relevant implementation and tests.