fix(swift): Enable wire tests for Swift SDK exhaustive fixture

[jsklan]

Description

Refs: Request from @jsklan

Link to Devin run

Enables wire tests for the Swift SDK exhaustive fixture by fixing several issues in the dynamic snippet generator and wire test generator.

Changes Made

Swift Dynamic Snippets (EndpointSnippetGenerator.ts)

• Added endpoint-level header handling that filters out service-level headers (service-level headers are handled at client constructor level, not in endpoint method calls)
• Fixed referenced body types to be passed directly instead of wrapped in .init(body: ...)

Swift Dynamic Snippets (DynamicTypeLiteralMapper.ts)

• Added comprehensive JSONValue conversion system for set types (Swift sets are represented as JSONValue.array([...]))
• Handles nested types within sets including primitives, objects, lists, and optionals

Swift Wire Test Generator (WireTestFunctionGenerator.ts)

• Fixed enum and union types to use full type names (e.g., Animal.dog instead of .dog) for proper Swift type inference
• Fixed set types to use JSONValue conversion in test assertions
• Fixed response body formatting to distinguish between string responses (raw UTF-8) and other types (JSON-encoded) - this matches how the Swift SDK's HTTPClient handles different response types

Test Definitions

• Added user-specified examples to set<T> endpoints in exhaustive fixture to ensure autogenerated examples include request body values (with proper response fields)

Testing

• Seed tests pass for swift-sdk exhaustive fixture (including wire tests)
• Lint checks pass
• Swift dynamic snippets unit test snapshots updated
• IR generator test snapshots updated (examples.json, exhaustive.json)
• fern check passes for exhaustive fixture

Review Checklist

• Verify the JSONValue conversion in DynamicTypeLiteralMapper.ts handles all type cases correctly
• Check that isStringResponseType() in WireTestFunctionGenerator.ts correctly resolves type aliases
• Verify the service-level header filtering logic in EndpointSnippetGenerator.ts correctly identifies headers from this.context.ir.headers
• Verify referenced body type handling doesn't break other endpoints that use simple request bodies

Updates since last revision

• Reverted the dynamic IR change (DynamicSnippetsConverter.ts) that was filtering service-level headers at the IR level - this was breaking other generators (e.g., PHP SDK)
• Moved the service-level header filtering to the Swift dynamic snippet generator specifically (EndpointSnippetGenerator.ts), so it only affects Swift and not other generators
• Fixed biome formatting issue

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