[codex] cover dynamic import local candidates

[andrewtdiz]

Summary

Part of #1674.

This adds end-to-end Node parity coverage for dynamic import() specifiers stored in never-reassigned local let bindings with finite literal candidate sets.

• covers let specifier = flag ? "./a" : "./b"; await import(specifier) inside a function
• covers a transitive template-literal case where a never-reassigned local candidate feeds another local specifier
• adds two tiny fixture target modules so both dispatch branches are executed at runtime

The resolver support is already present on current main; this PR locks the behavior in the parity suite.

Non-goals

• no compiler/runtime behavior changes
• no template-glob/context-module wildcard expansion coverage in this cut
• no function-parameter type narrowing or later-assignment reaching-definition analysis

Validation

• npm exec --yes --package=node@26 -- node --experimental-strip-types test-parity/node-suite/module/loader/dynamic-import-local-candidates.ts
• CARGO_BUILD_JOBS=1 CARGO_TARGET_DIR=/tmp/perry-dynamic-import-build cargo build --release -p perry -p perry-runtime -p perry-stdlib
• PERRY_NO_AUTO_OPTIMIZE=1 /tmp/perry-dynamic-import-build/release/perry test-parity/node-suite/module/loader/dynamic-import-local-candidates.ts -o /tmp/perry_dynamic_import_local && /tmp/perry_dynamic_import_local
• PERRY_NO_AUTO_OPTIMIZE=1 CARGO_TARGET_DIR=/tmp/perry-dynamic-import-build npm exec --yes --package=node@26 -- bash -lc './run_parity_tests.sh --suite node-suite --module module --filter dynamic-import-local-candidates'
• PERRY_NO_AUTO_OPTIMIZE=1 CARGO_TARGET_DIR=/tmp/perry-dynamic-import-build npm exec --yes --package=node@26 -- bash -lc './run_parity_tests.sh --suite node-suite --module module --filter dynamic-import'
• cargo fmt --all -- --check
• git diff --check
• ./scripts/check_file_size.sh