FIX: use max_iterations in CharSwapConverter perturbation loop

[KutalVolkan]

Description

Fixes #1259

The max_iterations parameter was validated and stored but never used in the perturbation loop.

Changes

• Fixed _perturb_word() to iterate max_iterations times before returning
• Added parametrized test to verify max_iterations affects output
• Updated notebook documentation to explain both max_iterations and proportion parameters

cc @romanlutz

[romanlutz]

Thank you for fixing this and for adding the extra test. (And so fast!)

It's a pleasure to collaborate with you, as always 🙂

[KutalVolkan]

Thank you for fixing this and for adding the extra test. (And so fast!)

It's a pleasure to collaborate with you, as always 🙂

Thanks Roman! Well, I introduced the bug in the first place, so only fair I fix it 😅 Always a pleasure collaborating with you too!