[api] Add .getNonPrimitiveType() getter

[mrazauskas]

Close #2850

This PR adds the missing .getNonPrimitiveType() getter.

[Copilot]

Pull request overview

Adds the missing getNonPrimitiveType intrinsic type getter to the native TypeScript-Go API surface, aligning the checker intrinsic getters with upstream/Strada expectations (issue #2850).

Changes:

• Exposes Checker.GetNonPrimitiveType() from the Go checker (c.nonPrimitiveType).
• Wires a new API method (getNonPrimitiveType) through the server protocol + request handler.
• Adds sync/async native-preview client methods and coverage in both sync/async API test suites.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/checker/exports.go	Adds exported Go checker getter GetNonPrimitiveType() returning c.nonPrimitiveType.
internal/api/session.go	Routes getNonPrimitiveType requests to the intrinsic-type handler using the new checker getter.
internal/api/proto.go	Adds MethodGetNonPrimitiveType constant and registers its params unmarshaller.
_packages/native-preview/src/api/sync/api.ts	Adds checker.getNonPrimitiveType() to the sync client wrapper.
_packages/native-preview/src/api/async/api.ts	Adds checker.getNonPrimitiveType() to the async client wrapper.
_packages/native-preview/test/sync/api.test.ts	Adds a test asserting returned type includes TypeFlags.NonPrimitive.
_packages/native-preview/test/async/api.test.ts	Adds the async equivalent test for TypeFlags.NonPrimitive.