perf: Field.toEuclideanDomain fast_instance%

[kbuzzard]

---

Just an experiment. Pulled this fast_instance% off #38087 to see if it makes a difference. Will then try it after #39263 to see if it still makes a difference.

[kbuzzard]

!radar

[leanprover-radar]

Benchmark results for 0d7dd61 against bcb9e00 are in. No significant results found. @kbuzzard

• ✅ build//instructions: -56.8G (-0.03%)

Small changes (6✅)

• ✅ build/module/Mathlib.Algebra.Lie.Weights.Killing//instructions: -1.4G (-1.17%)
• ✅ build/module/Mathlib.Algebra.Lie.Weights.RootSystem//instructions: -1.5G (-1.54%)
• ✅ build/module/Mathlib.FieldTheory.Galois.NormalBasis//instructions: -473.2M (-1.77%)
• ✅ build/module/Mathlib.FieldTheory.LinearDisjoint//instructions: -2.3G (-1.47%)
• ✅ build/module/Mathlib.RingTheory.LaurentSeries//instructions: -4.7G (-1.87%)
• ✅ build/module/Mathlib.RingTheory.Spectrum.Prime.Homeomorph//instructions: -455.4M (-1.70%)

[github-actions]

PR summary 4529a2df72

Import changes for modified files

Dependency changes

File	Base Count	Head Count	Change
Mathlib.Algebra.EuclideanDomain.Field	184	185	+1 (+0.54%)

Import changes for all files

Files	Import difference
Mathlib.Algebra.EuclideanDomain.Field	1

---

Declarations diff

+ instance (priority := 100) toEuclideanDomain : EuclideanDomain K := fast_instance%
- instance (priority := 100) toEuclideanDomain : EuclideanDomain K

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.

---

No changes to strong technical debt.

No changes to weak technical debt.

[kbuzzard]

Master now has #39263 so let's see if that makes a different (I suspect it will)

!radar

[leanprover-radar]

Benchmarking 4529a2d against ec05634 (preliminary results).

_{React with 👀 to be notified when the results are in. The command author is always notified.}