Closes #293.

Problem

The visitor currently treats packages loaded via Node's register hook as unused. The OP's repro:

// resources/loaders/ts.js
import { register } from 'node:module';
import { pathToFileURL } from 'node:url';

register('@swc-node/register/esm', pathToFileURL('./'));

// package.json
{
  "devDependencies": { "@swc-node/register": "1.11.1" },
  "scripts": { "test-script": "node --import ./resources/loaders/ts.js ./test-script.ts" }
}

fallow dead-code flags @swc-node/register as unused even though it is loaded by specifier at runtime.

Fix

When a register(...) call is bound to the register export of node:module (or the unprefixed module), record the first-argument specifier as a DynamicImportInfo. The graph layer already credits the resolving package via ResolveResult::NpmPackage, so @swc-node/register/esm flows back to @swc-node/register in package.json.

Recognised forms:

// named
import { register } from 'node:module';
register('@swc-node/register/esm', pathToFileURL('./'));

// aliased
import { register as registerLoader } from 'node:module';
registerLoader('tsx/esm', import.meta.url);

// namespace
import * as Module from 'node:module';
Module.register('@swc-node/register/esm', import.meta.url);

Unrelated register(...) functions imported from anything other than node:module are not affected. Non-string first arguments (register(loaderUrl, ...)) are also ignored, matching how the visitor handles import(variable).

Tests

• 7 new unit tests in crates/extract/src/tests/js_ts/dynamic_imports.rs covering named + aliased + namespace forms, the unprefixed module specifier, template-literal first-argument, the negative case (register from another module is not credited), and the dynamic-first-argument case (no entry recorded).
• 1 new integration test in crates/core/tests/integration_test/false_positive_fixes.rs reproducing the OP's setup end-to-end and asserting @swc-node/register is not in unused_dev_dependencies.

Full suites green locally:

• cargo test -p fallow-extract --lib — 1399 passed.
• cargo test -p fallow-core --test integration_test false_positive_fixes — 16 passed.
• cargo test -p fallow-cli --bin fallow — 1755 passed.

Notes

• Imports are recorded during the same AST walk before the call is visited, and ESM hoists imports to the top of the module, so the visit-time check is sufficient for real-world code (mirrors how vi.mock and customElements.define are handled).
• Aligned with the existing vitest_mock_source / extract_custom_elements_define style: a small free helper for the specifier extraction plus a method on ModuleInfoExtractor for the import-binding lookup.