fix(compile): #684 — type-only imports must not load as runtime modules

[proggeramlug]

Summary

The module collector iterated every hir_module.imports entry through cached_resolve_import and queued them all as runtime modules, ignoring import.type_only. So import type { … } from \"…\" triggered V8 fallback for type-only packages, and any access to the (non-existent) named imports during init threw TypeError.

Deterministic repro

bun add effect@3.21.2
echo 'import {} from \"effect\"; console.log(\"ok\")' > test.ts
perry compile test.ts -o /tmp/out
/tmp/out
# before:  TypeError: Cannot read properties of undefined (reading '_tag')

Effect's Schema.ts has exactly one @standard-schema/spec reference — import type { StandardSchemaV1 } from \"@standard-schema/spec\". The package ships an empty var src_exports = {} at runtime (type-only by design). The collector saw the import and routed the package through V8 (only JS module among 363), so any <StandardSchemaV1>._tag read inside Effect's compiled code threw V8's exact wording. That uncaught TypeError is the #684 symptom in its current form — the original (number).slice message dissolved once intervening landings advanced Effect's init past the old crash point.

Fix

One guard at the top of the import-processing loop in collect_modules.rs — skip entries with type_only: true. Class-metadata flow is unaffected: the HIR layer at lower.rs:4151 already captures type-only specifiers into imported_classes for method dispatch (#446 path). The collector only governs whether the module's .o (or JS bundle) participates in linking and runtime init.

Test plan

• import type { Foo } from \"./does_not_exist\" now compiles cleanly (was rejected at the resolve step).
• Mixed import { x } + import type { T } from the same file still resolves the value side correctly.
• cargo test --release -p perry-hir -p perry-codegen -p perry — all green (223 + 29 + 4 + 41 + 1 + 40 + 10 + 6, 0 failed).
• 7-test class+import smoke set byte-identical to node --experimental-strip-types.
• cargo fmt --all -- --check — clean.

Follow-up

The Effect repro now advances past the _tag crash and exposes a separate link-time gap: js_readable_stream_* symbols are unresolved because Effect uses the global ReadableStream constructor (no literal import \"streams\"), and compute_required_features only triggers bundled-streams on the named import. Auto-enabling the streams feature on global new ReadableStream() / new WritableStream() / new TransformStream() is a separate Effect-e2e (#321) follow-up.

Closes #684.