alts: move ParseFramedMsg out of common

[kevinGC]

It's only called in one place, and is effectively a method on conn.

Part of #8510.

Note that this PR includes #8509. GitHub doesn't support proper commit chains / stacked PRs, so I'm doing this in several PRs with some (annoyingly) redundant commits. Let me know if this isn't a good workflow for you and I'll change things up.

RELEASE NOTES: N/A

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.85%. Comparing base (55e8b90) to head (9efdb0d).
⚠️ Report is 20 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8511      +/-   ##
==========================================
- Coverage   82.40%   81.85%   -0.56%     
==========================================
  Files         414      413       -1     
  Lines       40531    40520      -11     
==========================================
- Hits        33399    33167     -232     
- Misses       5770     5982     +212     
- Partials     1362     1371       +9     

Files with missing lines	Coverage Δ
credentials/alts/internal/conn/common.go	100.00% <ø> (ø)
credentials/alts/internal/conn/record.go	81.00% <100.00%> (+2.80%)	⬆️

... and 43 files with indirect coverage changes

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[arjan-bal]

Note that this PR includes #8509. GitHub doesn't support proper commit chains / stacked PRs, so I'm doing this in several PRs with some (annoyingly) redundant commits. Let me know if this isn't a good workflow for you and I'll change things up.

@kevinGC, it would be great if you could rebase this branch off of master so both PRs can be merged independently. We shouldn't need Go 1.24 for the changes in this PR.

[arjan-bal]

LGTM, with request to remove the Go 1.24 changes. Adding a reviewer from the security team.

[gtcooke94]

I think the easiest way for reviewers to diff is to just get the prior PRs merged and then this will diff nicely against master

The other option is to make a PR on your fork against the other PR branch if you want us to see the diff right now, then eventually open a PR later

[gtcooke94]

At a glance I personally prefer the previous style of returning nextFrame and not modifying state in this method, I think it makes it easier to follow and test. Do we have a compelling reason to swap it to this?

[kevinGC]

I'm happy to leave as-is or revert back to the old version. It just seemed odd to have a function in common.go that's only called in 1 place and always called s.t. it modifies the same bit of struct state.

Happy with whatever the gRPC team wants -- this was more of an implementation detail on the way to my other changes.

[arjan-bal]

Deferring to the @gtcooke94 since the security team owns this package. Closing the PR.

[kevinGC]

Rebased. Looks like there're differing opinions on whether this is change is worth making -- I'm cool with keeping or dropping it.