refactor(NumberTheory): golf Mathlib/NumberTheory/PythagoreanTriples

[yuanyi-350]

• simplifies the Int.gcd x y = 0 branches in gcd_dvd, normalize, and classified using Int.gcd_eq_zero_iff
• shortens the zero case in normalize to a direct simpa from PythagoreanTriple.zero

Extracted from #38144

[github-actions]

PR summary e18244a4f1

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

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

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

The doc-module for scripts/pr_summary/declarations_diff.sh contains some details about this script.

---

No changes to technical debt.

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[yuanyi-350]

I ran a profiler comparison for the changed declarations in this PR.

Results (seconds):

• PythagoreanTriple.gcd_dvd: 0.113373 -> 0.124069 (+9.43%)
• PythagoreanTriple.normalize: 0.109086 -> 0.217934 (+99.79%)
• PythagoreanTriple.classified: 0.025653 -> 0.022601 (-11.90%)

Overall:

• classified is a bit faster
• gcd_dvd regresses slightly
• normalize regresses substantially and dominates the overall change

[yuanyi-350]

!bench

[leanprover-radar]

Benchmark results for dcb553d against e18244a are in. No significant results found. @yuanyi-350

• ✅ build//instructions: -11.2G (-0.01%)

No significant changes detected.

[MichaelStollBayreuth]

maintainer merge

[github-actions]

🚀 Pull request has been placed on the maintainer queue by MichaelStollBayreuth.