chore: Divide testing into PR validation and release readiness workflows

[scouten-adobe]

PR validation (aka "CI") should be MUCH faster now since we're only running on ubuntu-latest.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.99%. Comparing base (60001a7) to head (9a9bdec).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1281      +/-   ##
==========================================
- Coverage   80.07%   77.99%   -2.08%     
==========================================
  Files         151      150       -1     
  Lines       43401    38328    -5073     
==========================================
- Hits        34752    29895    -4857     
+ Misses       8649     8433     -216     

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[dyro]

The linux jobs seem to complete pretty quickly, sans the tests using cross. Should we try switching to aarch64 linux runners before removing tests from our PR checks?

[scouten-adobe]

@dyro my counter-argument is that we have very few platform-specific issues (except for Wasm/WASI, which are unfortunately slow to run). My goal here is to run as few tests as possible on the fastest possible platform to catch the most common issues.

[dyro]

@scouten-adobe : Understood. I think keeping as much as we can in the PR runner will eliminate headaches when we go to release, especially since our releases can occur far apart from each other. However, I don't do much work in c2pa-rs, so I don't want my opinion to sway the decision to split up our PR checks. Also, I can run the pre-release runner manually when I do contribute 👍

[gpeacock]

We should update the makefile so that we have a make ci and make release option, or something along that line, allowing us to pre-check or test locally.

[scouten-adobe]

@gpeacock as an alternative to your Makefile suggestion, I've added a new label "check-release" which you can apply to any PR to invoke the full release-readiness test suite. (IMHO the Makefile approach is necessarily incomplete because we need to be able to run on multiple platforms and you can't do that on any laptop.)