[Vardhman Gupta (Kaap10)]

Description

Closes #3401

Adds a configurable safe parameter to UrlConverter:

• Default safe="": Enforces complete URL encoding of reserved characters by default, including forward slashes (/ -> %2F), ensuring path traversal (../../etc/passwd) and SSRF payloads are properly encoded for evasion testing.
• Custom safe Support: Callers wishing to preserve specific characters (such as / or /:) can configure UrlConverter(safe="/") or any custom string.
• Identifiable & Serialization: Overrides _build_identifier() to serialize params={"safe": self._safe}, adhering to the converter contract.
• Input Validation: Validates that safe is a string, raising TypeError otherwise.

Tests and Documentation

• Added test_url_converter_default_encodes_forward_slash verifying that path traversal and SSRF payloads have slashes encoded as %2F by default.
• Added test_url_converter_custom_safe testing safe="/", safe="/:", and query formatting safe="?=".
• Added test_url_converter_property_and_identifier testing the property and identifier parameter serialization.
• Added test_url_converter_invalid_safe_type verifying TypeError on invalid arguments.
• Added test_url_converter_reconstruction verifying reconstruction parameters.
• Ran converter unit tests and contracts: all 192 tests pass; ruff check and format pass.