fix: do not panic on duplicate height and priority

[Tyagiquamar]

Summary

• Stop panicking in resolvePriorities when two upgrade or version entries share the same height and priority. That panic currently kills the Blazar process from the upgrade proposals watcher.
• If the tags match, collapse the duplicate (LOCAL over DATABASE over CHAIN) and keep the loser in the overridden list.
• If the tags differ, return an error so the watcher can log it and keep running instead of crashing.

Fixes #56

Test plan

• Unpatched TestSimultaneousProviders still asserts the panic on main.
• go test -mod=readonly -count=1 ./internal/pkg/upgrades_registry in golang:1.24-bookworm (PASS, 0.106s)
• go test -mod=readonly -race -count=1 ./internal/pkg/upgrades_registry in golang:1.24-bookworm (PASS, 1.314s)

[Tyagiquamar]

Hi, just following up on this when you get a chance. The branch is up to date and checks are green. If it looks good from your side, it should be ready to merge. Happy to make any changes if needed. Thanks!

[qezz]

Hi @Tyagiquamar

We appreciate the contribution. It will take some time to review the patch.

Also, please let us know what % of the code has been generated by the LLM.

Thanks!

[Tyagiquamar]

100% of the code in this PR was generated by an LLM. Thank you for reviewing it when you have time.