[http-specs] Add named-model query parameter scenario to remaining expansion styles for parity

[JoshLove-msft]

Background

PR #11125 added a model (named model value) scenario for query parameter expansion, but only under query-expansion/explode:

• Routes_QueryParameters_QueryExpansion_Explode_model — GET /routes/query/query-expansion/explode/model?field=status&value=active

This covers the gap behind #11123 / #10973, where a named model flows through a different emitter type-handling path than a Record<T>.

Request

For parity with the existing primitive / array / record cases, add the same named-model scenario to the other expansion styles that currently lack it:

• query-expansion/standard ({?param})
• query-continuation/standard (?fixed=true{&param})
• query-continuation/explode (?fixed=true{&param*})

Each should use a named model value (e.g. ExpandParameters { field: string; value: string; }) and add a matching mock API plus regenerated spec-summary.md.

Follow-up requested in PR #11125 review.

[github-actions]

🎯 Issue Triage

Feature request to extend the @typespec/http-specs test suite with named-model query parameter scenarios across three expansion styles (query-expansion/standard, query-continuation/standard, query-continuation/explode) to match the explode variant added in PR #11125.

Category: Feature Request
Area: lib:http-specs

🔍 Analysis

• PR [http-specs] Add explode object query parameter Spector scenario #11125 added a model scenario for query-expansion/explode, covering the gap identified in [Bug]: C# client emits wrong query string for @query(#{explode: true}) on nested object models #11123 / [Bug]: query params with nested objects are encoded wrong #10973 where named models take a different emitter type-handling path than Record<T>.
• The three remaining expansion styles (query-expansion/standard, query-continuation/standard, query-continuation/explode) currently have primitive, array, and record scenarios but no named-model scenario.
• The work involves adding a new ExpandParameters { field: string; value: string; } model, the corresponding route ops with the appropriate @query expansion decorators, mock API handlers, and regenerating spec-summary.md for each of the three styles.
• This is a well-scoped, self-contained contribution that closely mirrors the existing pattern from PR [http-specs] Add explode object query parameter Spector scenario #11125.

📝 Suggested next steps

• Add model scenario to query-expansion/standard using {?param} style
• Add model scenario to query-continuation/standard using ?fixed=true{&param} style
• Add model scenario to query-continuation/explode using ?fixed=true{&param*} style
• Add mock API handlers for each new scenario
• Regenerate spec-summary.md

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