std tightens YAML, dotenv, and data-structure APIs

API polish across data structures and YAML

RollingCounter was brought closer to the other unstable data-structure APIs with explicit iteration, readonly snapshots, at() and toArray(), plus stricter restore-time validation. In YAML, parse()/parseAll() now have sharper SyntaxError typing and parseAll() returns unknown[], making the contract clearer for multi-document input and invalid YAML failures.

YAML parsing got a faster, safer mapping write path

The YAML loader now writes ordinary mapping keys via direct property assignment instead of Object.defineProperty, which should reduce V8 overhead during parse and merge operations. The special __proto__ case still uses the slower descriptor path to avoid prototype pollution, and new regression tests cover merge keys and __proto__ handling.

Dotenv now round-trips escapes more faithfully

stringify() was updated to preserve literal backslash escape sequences before newline, carriage return, and tab characters, while parse() now accepts escaped quotes and backslashes inside double-quoted values. Together, these changes fix a class of round-trip bugs where quoted values or escape-like text would be altered on write/read cycles.

Other misc changes

• Clarified path docs for basename, dirname, and extname, especially around URL handling.
• Added @throws notes and guidance for non-file: URLs in posix/windows path docs.