streamich/memfs

AI Summary: This issue proposes allowing users to inject a custom `process` object into `memfs` to improve testability. Currently, `memfs` relies on the global Node.js `process` object, making it difficult to mock and leading to potential test leakage. By enabling custom `process` implementations, tests can be more isolated, deterministic, and simulate different environments without altering global state.

AI Summary: The task is to debug and fix a bug in the `memfs` library where read-only file system operations (like `fs.statSync` and `readdirSync`) unexpectedly modify the modification time (`mtime`) of parent directories. The root cause has been identified as an unconditional timestamp update within the `Link.prototype.getChild` method, which needs to be corrected to only update the timestamp during write operations.