fix(swift): allow Sendable conformance with objective-c-support

[schani]

Bug

With --sendable --objective-c-support, generated Swift types lost Sendable conformance entirely — even enums, which have no NSObject/Objective-C interop concern at all.

Repro (from issue #2781, using the maintainer triage's schema/flags):

node dist/index.js --lang swift --src-lang schema --src example.schema.json \
  --sendable --struct-or-class class --objective-c-support --top-level Example

Before: @objcMembers class Example: NSObject, Codable { ... } and enum Fruit: String, Codable { ... } — zero occurrences of Sendable.

Without --objective-c-support, the same input correctly produced class Example: Codable, Sendable and enum Fruit: String, Codable, Sendable.

Root cause

getProtocolsArray in packages/quicktype-core/src/language/Swift/SwiftRenderer.ts unconditionally dropped Sendable whenever objcSupport was enabled, regardless of declaration kind (class/struct/enum). Enums and structs have no NSObject interop concern, so the guard was over-broad. For classes, Swift does allow Sendable conformance on an NSObject subclass provided the class is final and has only immutable, Sendable stored properties.

Fix

• Dropped the blanket !this._options.objcSupport guard in getProtocolsArray, so Sendable is added whenever --sendable is set and (for classes) properties are immutable — independent of objcSupport.
• When emitting a class declaration, also emit final whenever sendable is on and properties are immutable (in addition to the existing finalClasses option), since Swift requires NSObject subclasses to be final to conform to Sendable.
• Classes with --mutable-properties remain non-Sendable/non-final, matching existing (correct) behavior without --objective-c-support.

Test coverage

Added a new fixture, swift-sendable-objective-c (test/languages.ts / test/fixtures.ts), that generates Swift with --sendable --struct-or-class class --objective-c-support (plus a struct-or-class: struct variant via quickTestRendererOptions) and runs a small verification script (test/fixtures/swift/verify-sendable.cjs) asserting every generated class/struct/enum declaration includes Sendable, and that Sendable classes are emitted @objcMembers final class.

Real swiftc compilation isn't available in this environment (and the existing swift/schema-swift fixtures are already disabled in CI's test-pr.yaml due to a pre-existing "pgp issue"), so this fixture verifies the generated source text directly rather than compiling/running it, following the same includeJSON/custom-compileCommand pattern already used elsewhere in test/languages.ts (e.g. the nbl-stats.json-scoped fixtures).

Verification performed locally

• Confirmed the new fixture fails (exit 1, Generated type is not Sendable) against the pre-fix renderer, and passes after the fix.
• QUICKTEST=true FIXTURE=swift-sendable-objective-c script/test passes.
• npm run test:unit — 169/169 tests pass.
• npm run lint (biome) — clean.
• npm run build — passes.
• Manually re-ran the issue's repro command and confirmed correct output for class+immutable, class+mutable-properties, and struct cases.

Fixes #2781

🤖 Generated with Claude Code