fix: use pointer receivers for piped protobuf models

[srinivasr]

What this PR does:
generated protobuf structs like applicationsyncstate embed a sync.mutex. because their methods were using value receivers, the lock state was being copied every time they were called or passed around (flagged by go vet).

fix:

• change methods on applicationsyncstate and applicationlivestateversion to use pointer receivers
• update all caller sites in driftdetector and livestatestore to pass pointers
• convert range loops in tests to index loops to avoid copying test structs

Why we need it:
passing mutexes by value creates silent data races under concurrent execution because the copies do not block each other.

Which issue(s) this PR fixes:

Fixes # N/A

Does this PR introduce a user-facing change?:

• How are users affected by this change: no user-facing change.
• Is this breaking change: no.
• How to migrate (if breaking change): n/a

[github-actions]

👋 Hi @srinivasr, welcome to PipeCD and thanks for opening your first pull request!

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[areebahmeddd]

i don’t think this branch compiles .. you should run go build ./... and make check locally

[srinivasr]

i don’t think this branch compiles .. you should run go build ./... and make check locally

you're right, i missed a caller in builder.go when i was switching the models to use pointer receivers. i just pushed a fix and verified it builds cleanly locally now

[srinivasr]

sorry for the delay on this. merged master in (it has #7137 now which touches the same HasDiff func, both changes work together fine) and squashed the branch while I was at it since the history had piled up fixups, so commit dates show today. doc comment is back and the unrelated reflector_test change is reverted as discussed

also pulled the metadatastore race fix out of this PR into its own branch to keep this one focused on what was reviewed.

[areebahmeddd]

looks good. maybe @khanhtc1202 will give a final look and merge 🙂

[armistcxy]

LGTM, there one place I think you should add comment on top of that line

[armistcxy]

Special thanks to @areebahmeddd for helping with the review 💯

[armistcxy]

LGTM

[github-actions]

Thank you for contributing to PipeCD, @srinivasr! The changes in this pull request will be part of the upcoming release!