Add CRC mode to make CRC checks opt-in by default

[samypr100]

Summary

This is a POC quick fix as proposed in #12618 (comment)

This adds a UV_CRC_MODE env var that allows enforce or lax to be set or default to none which does nothing.

Avoided reworking out the interfaces as that led to a larger change across uv-extract and uv-metadata, but longer term that's probably a better solution.

Looking at the dependency graph, uv-distribution-filename was sort-off the best place for CRC Mode, but I'd be happy to move it.

Test Plan

Updated existing crc test.

[charliermarsh]

LGTM.

[charliermarsh]

We should probably make this a global setting so it shows up in settings, etc. But I know that's more work, can be a TODO.

[zanieb]

I'm curious why not "Error" and "Warn" here which feel more canonical to me?

[zanieb]

(which would also be "Ignore" instead of "None", I think)

[zanieb]

I wonder if we'd then want a different name? UV_CRC_CHECK = error | warn | ignore? I feel less strongly about that.

[samypr100]

Happy to do the change once I'm back to personal laptop

[Gankra]

I'm gonna put up a PR for an alternative approach.

[Gankra]

I'm going to close this in favour of #12722, but if that fix proves insufficient this is a more robust hammer we should revisit.

[zanieb]

Thanks for hoping on this anyway Sam.