v1.16: moves new_warmup_cooldown_rate_epoch outside iterators and for loops (backport of #33259)

[mergify]

This is an automatic backport of pull request #33259 done by Mergify.
Cherry-pick of c1090d3 has failed:

On branch mergify/bp/v1.16/pr-33259
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Changes to be committed:
	modified:   programs/stake/src/stake_instruction.rs
	modified:   sdk/src/feature_set.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   programs/stake/src/stake_state.rs
	both modified:   runtime/src/bank.rs

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[behzadnouri]

Backporting this not to introduce any performance regression in the epoch boundary rewards calculation.

[codecov]

Codecov Report

Merging #33262 (4b68eb8) into v1.16 (988641d) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            v1.16   #33262   +/-   ##
=======================================
  Coverage    81.9%    81.9%           
=======================================
  Files         762      762           
  Lines      207833   207835    +2     
=======================================
+ Hits       170320   170365   +45     
+ Misses      37513    37470   -43