Add Xquik REST example and encode path params

[kriptoburak]

Summary

• add a REST header-auth example that points API Agent at Xquik's public OpenAPI specification
• cover an OpenAPI 3.1 Xquik search endpoint, optional parameter filtering, and both supported auth schemes
• percent-encode REST path parameters so slashes, spaces, plus signs, and Unicode cannot alter route structure
• document the path-encoding correction in the changelog

Independent Repository Fix

The REST URL builder previously inserted path parameter values verbatim. A value such as alice/bob + team could change path segments or produce an invalid URL. The client now percent-encodes each substituted value and includes focused regression coverage.

Duplicate Check

• checked existing open and closed PRs in agoda-com/api-agent for Xquik and related package names

Validation

• uv lock --check
• uv run ruff check api_agent/ tests/
• uv run ruff format --check api_agent/ tests/
• uv run ty check
• uv run pytest tests/test_rest_client.py tests/test_rest_schema.py -q - 51 passed
• uv run pytest tests/ -q - 341 passed
• git diff --check

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