[py] translate continue_request/continue_response kwargs to BiDi wire format

[AutomatedTester]

🔗 Related Issues

Follow-up to #17666 (both address kwargs handling in the high-level driver.network API).

💥 What does this PR do?

Fixes the high-level Request.continue_request and Response.continue_response so their keyword arguments are translated to the BiDi wire format instead of being passed through raw.

Previously both methods accepted **kwargs and merged them straight onto the wire params (params.update(kwargs)). That bypassed the snake_case → camelCase translation (status → statusCode, reason_phrase → reasonPhrase) and the value encoders (dict_to_headers, list_to_cookie_headers, _encode_bytes_value) used everywhere else in this layer. As a result, pythonic calls such as continue_response(status=503) or continue_request(headers={...}) silently sent the wrong key or an untranslated value — only undocumented raw wire keys actually worked.

🔧 Implementation Notes

• Replaced the **kwargs signatures with explicit, keyword-only params matching the existing set_* mutators:
  • continue_request(*, url, method, headers, cookies, body)
  • continue_response(*, status, reason_phrase, headers, cookies)
• _continue_params now overlays the explicit overrides on top of recorded mutations and runs everything through the same translation path, so explicit args get the correct wire keys/encoding and still override recorded mutations.
• No internal or test caller passed kwargs to either method (every call site is argument-less), so the keyword-only signature change is safe. These are the new, not-yet-released high-level BiDi APIs.

Added unit regression tests asserting explicit args are translated to wire format and that they override recorded mutations.

🧪 Testing

bazel test //py:test/unit/selenium/webdriver/common/bidi_network_tests-unit passes.

🤖 AI assistance

• No substantial AI assistance used
• AI assisted (complete below)
  • Tool(s): Claude Code (Opus 4.8)
  • What was generated: the fix and its regression tests
  • I reviewed all AI output and can explain the change

🔄 Types of changes

• Bug fix (backwards compatible)