merge: move the filtering of ambiguous files to a dedicated function I have multiple reasons: - The body of `_update` is way too long - This adds typing which will help our tooling and brains understand this code more easily - This function will get more nested and complex in the next patch I've taken the liberty of rewrapping and typo-passing the docstring.

timestamp: make the reliable comparison more usable from outside This is going to be used with pre-computed times unlike in status.

timestamp: add type information to the module This is easy to do and helps both Pytype and developpers understand what objects they are dealing with.

rust-dirstate: make the reliable timestamp comparison more usable from outside This is going to be used with pre-computed times unlike in status.

rust-dirstate-map: use a more precise identity This is closer to the behavior of what Python does. So far, we were checking only the inode, but this might not be good enough for the v1 case.

dirstate-map: add a missing debug wait point when accessing the v2 docket fc8e37c380d3 added synchronization points to the dirstate to allow for race condition testing without actually requiring a time-based race condition to happen. This changes adds the `pre-read-file` wait point before we read the docket, since callers might ask for the parents before anything else is read, leading to the first read being done before the wait point. This removes some differences in test output which were presumed to be speed related, but weren't.

rust-parsers: use the same error message as with the higher-level code This can happen at two places, but it's not really enough time to justify it being refactored. Let's ensure we have the same error message, the newer one being slightly more helpful.

rust-pathauditor: make sure we actually test the nested repo case This covers the *on-disk* case, where the path itself does not have a `.hg` component.

rust-pathauditor: match more of Python's behavior and display messages We will make use of the path auditor when running our update fast-path, and we want to output of it to be close enough.

rust-dirstate: pass dirstate tracked key from the requirements We will make use of this with the `hg update` fastpath