fix(openapi_fdw): respect quoted strings and escapes in Link header

[Vishv07]

Summary

Fixes an RFC 8288 parameter parsing bug in openapi_fdw/src/response.rs where a semicolon inside a quoted parameter value (such as title="item;rel=next") was treated as a top-level parameter delimiter, causing has_rel_next() to falsely identify the link entry as having rel="next".

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Problem

In split_link_entries(), entries are split on commas while carefully respecting quoted strings and RFC 7230 backslash escapes (\").

However, has_rel_next() previously split parameters using a plain params.split(';'). When a quoted parameter contained a semicolon and the substring
rel=next (e.g. <https://api.example.com/items>; title="page;rel=next"; rel="last"):

1. split(';') split the parameter into fragments title="page and rel=next".
2. split_once('=') matched name="rel", and trim_matches('"') produced value="next".
3. has_rel_next() returned true, incorrectly treating a rel="last" URL as the next pagination page.

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Solution

• Added split_link_params(), which splits parameter lists on top-level semicolons while honoring quoted strings and RFC 7230 quoted-pair backslash escapes
  (mirroring the entry splitting behavior in split_link_entries()).
• Updated has_rel_next() to iterate over split_link_params(params) instead of params.split(';').
• Added unit regression tests in response_tests.rs covering:
  • Quoted semicolons in non-rel parameters (e.g. title="a;rel=next"; rel="last" returning None).
  • Quoted semicolons with valid rel="next" parameters present.
  • Backslash-escaped quotes inside parameters (e.g. title="item \"foo;bar\""; rel="next").

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Verification

• Regression test reproduces the failure on main and passes with this fix.
• Full make check suite in wasm-wrappers/fdw/openapi_fdw passes cleanly:
  • cargo fmt clean
  • cargo clippy --all --tests --no-deps with 0 warnings
  • All 566 unit tests passing
  • cargo component build --release --target wasm32-unknown-unknown succeeds