Fix query parameters being silently dropped from HTTP requests

[dcrockwell]

Summary

• Query parameters set via the .query() builder were silently dropped from all outgoing HTTP requests — the server never received them
• Fixed two independent URL construction sites that both omitted the query string
• Fixed the mock server's GET /get endpoint to actually echo query parameters (was documented but never implemented)
• Added 8 regression tests with exact assertions covering all execution modes

Why

The .query("key=value") builder function correctly stored the query string internally, but the final step that assembled the URL for the actual HTTP request never included it. Any user relying on .query() to pass query parameters to a server was sending requests without them — with no error or warning. This affected all three ways to make a request: blocking, yielder streaming, and callback streaming.

What

Two bug fixes in the HTTP client:

The URL was assembled in two separate places in the codebase, and both had the same omission. One is used by send() and start_stream(), the other by stream_yielder(). Both now append ?query_string to the URL when query parameters are present.

One fix in the mock server:

The GET /get endpoint was documented as echoing query parameters since v1.0.0, but the implementation only used request.path — the query string was ignored. This is why no existing test could have caught the client bug. Now the endpoint includes a "query" field in its JSON response.

Eight regression tests:

All three execution modes are tested end-to-end against the mock server. Assertions parse the JSON response and do exact field matching (not substring checks). Additional tests cover URL-encoded special characters, empty query strings, and recorder record/playback round-trips with query parameters.

How

The fix itself is minimal — four lines of Gleam in each of the two URL construction sites:

let query_string = case request.query {
  option.Some(query) -> "?" <> query
  option.None -> ""
}

The query string is then concatenated onto the end of the assembled URL. When no query is set (the default), nothing changes.

Test plan

• All 185 tests pass (177 existing + 8 new)
• Mock server's 25 tests pass
• Pre-commit hooks pass (format check + full build across all modules and examples)
• send() delivers query params to server (exact JSON assertion)
• stream_yielder() delivers query params to server
• start_stream() delivers query params to server
• URL-encoded special characters arrive verbatim
• Empty query string edge case handled
• Recorder captures query in recordings
• Recorder playback matches by query string