[Merged by Bors] - feat(Valued/WithVal): missing rfl lemmas for field operations

[eric-wieser]

This adds the missing lemmas for (nat|int|nnrat|rat)Cast, zpow, and ofNat.

These were found while attempting a refactor to use Function.Injective.field in #39562.

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[github-actions]

PR summary bf95470997

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

+ ofVal_intCast
+ ofVal_natCast
+ ofVal_nnratCast
+ ofVal_ofNat
+ ofVal_ratCast
+ ofVal_zpow
+ toVal_intCast
+ toVal_natCast
+ toVal_nnratCast
+ toVal_ofNat
+ toVal_ratCast
+ toVal_zpow

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

## summary with just the declaration names:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

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No changes to strong technical debt.

No changes to weak technical debt.

[kbuzzard]

Thanks!

bors merge

[mathlib-bors]

Build failed:

• ci (staging) / Build

Fix if necessary, and then someone with permission can run bors r+ or bors retry.

[eric-wieser]

bors merge

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

• ci (staging) / Lint style
• ci (staging) / Build
• ci (staging) / Post-Build Step
• ci (staging) / Post-CI job