Update test_ratelimit.py to use latest draft syntax with RateLimit-Policy and RateLimit headers

[Copilot]

The test file was using outdated header syntax that didn't match the current draft specification. This PR updates all test cases to use the proper structured field format defined in the latest draft.

Changes Made

Updated Header Syntax:

• Before: limit=, remaining=, reset=, policy= (dictionary/simple values)
• After: RateLimit-Policy: "name";q=quota;w=window and RateLimit: "name";r=remaining;t=time (structured field lists)

Example of the transformation:

# Old syntax
headers = dict(
    policy="10;w=1,50;w=60,1000;w=3600",
    limit="1000"
)

# New syntax 
headers = dict(
    **{"RateLimit-Policy": '"hourly";q=1000;w=3600,"daily";q=5000;w=86400'},
    **{"RateLimit": '"hourly";r=999;t=3540'}
)

New Test Coverage:

• Basic policy and rate limit header parsing
• Multiple policies in a single header
• Partition key support with base64 encoding (pk=:base64data:)
• Quota units for different measurement types (qu="content-bytes")
• Policy lookup by name matching between headers
• All parameter types: q (quota), w (window), r (remaining), t (time), pk (partition key), qu (quota unit)

Modernized Functions:

• Replaced parse_fields() with parse_ratelimit_headers()
• Updated find_quota_policy() to find_policy_by_name() for name-based lookups
• Added comprehensive test runner with clear pass/fail reporting

All tests pass and the file now fully complies with the latest IETF draft specification for RateLimit headers.

Fixes #153.

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