test: extract edge cases to separate file

Splits purl-edge-cases.test.mts (202 tests) from package-url.test.mts
to improve test organization. Covers URL scheme handling, component
validation, special character handling, version separators, subpath/
qualifier handling, type-specific normalizations, round-trip consistency,
error messages, prototype pollution prevention, and memory/performance tests.

Deletes unused scripts/utils/trash.mjs with broken 'trash' package import.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: jdalton