[WIP]Implement reproducible out/ folder contents across different filesystem layouts

[rahat2134]

This PR addresses issue #3660 by making the out/ folder contents more reproducible and filesystem layout agnostic. These changes allow for re-using the out/ folder as a build cache between different machines, supporting both coarse-grained (e.g., zip file transfer) and fine-grained (via Bazel remote cache protocol) caching strategies.

Key Changes:

• Updated PathRef to normalize paths relative to workspace, Coursier cache, and home directory
• Implemented NonDeterministicFiles to handle non-deterministic file content
• Updated JsonFormatters to use the new path normalization methods
• Added integration test ReproducibleOutTest to verify reproducibility
• Updated build.mill in the integration test to define the necessary project structure

Reproducibility is achieved by:

1. Normalizing paths in serialized PathRefs
2. Handling non-deterministic files (e.g., mill-profile.json, worker JSONs)
3. Zeroing out modification times for zip and jar files

Testing:

• Added new integration test ReproducibleOutTest
• Existing tests have been updated and pass

Documentation:

• Updated relevant comments in the code

Performance Impact:

• Initial testing shows minimal impact on build times, but more extensive performance testing may be needed for large projects

[rahat2134]

@lihaoyi, Can you take a top-level look at the changes and whether they are aligned with the solution or not in any way?
I am working on tests to pass.

(Also, If somehow you can tell why the tests are failing, it will be a great help!)
Thanks!

[lihaoyi]

@rahat2134 the top level changes look reasonable. The CI logs seem to be overloaded with all the printlns you added and won't load for me, you should try removing them and try to run the failing tests locally to debug further