chore(Algebra/QuadraticAlgebra): define all the casts through C

[xroblot]

The casts into QuadraticAlgebra R a b were defined in two different ways, some through C and some through the anonymous constructor, which made the Algebra ℤ instances non-defeq at instance transparency. Using C everywhere fixes it, and an example records the defeq.

Prepared with Claude Code 🤖

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[github-actions]

PR summary 121ba01f18

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff (regex)

+ instance : NNRatCast (QuadraticAlgebra K a b) where nnratCast q := .C q
+ instance : RatCast (QuadraticAlgebra K a b) where ratCast q := .C q
- instance : NNRatCast (QuadraticAlgebra K a b) where nnratCast q := ⟨q, 0⟩
- instance : RatCast (QuadraticAlgebra K a b) where ratCast q := ⟨q, 0⟩

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.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit 121ba01).

• +2 new declarations
• −4 removed declarations

-QuadraticAlgebra.im_nnratCast
-QuadraticAlgebra.im_ratCast
+QuadraticAlgebra.nnratCast_def
+QuadraticAlgebra.ratCast_def
-QuadraticAlgebra.re_nnratCast
-QuadraticAlgebra.re_ratCast

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No changes to strong technical debt.
No changes to weak technical debt.

Current commit 121ba01f18
Reference commit 9b46e33ce0

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.py 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).

[xroblot]

!radar

[jcommelin]

Thanks 🎉

bors merge

[mathlib-bors]

👎 Rejected by label

[jcommelin]

Whhops, too fast. But I do like the look of this.

[xroblot]

@jcommelin I still want to do some testing before merging this PR

[leanprover-radar]

Benchmark results for 40e78fb against 9b46e33 are in. No significant results found. @xroblot

• ✅ build//instructions: -1.4G (-0.00%)

No significant changes detected.

[xroblot]

@jcommelin Timings are fine so this PR is ready to be merged if you want to

[xroblot]

!radar

[leanprover-radar]

Benchmark results for 121ba01 against 9b46e33 are in. No significant results found. @xroblot

• 🟥 build//instructions: +22.0G (+0.02%)

Small changes (1🟥)

• 🟥 build/module/Mathlib.Algebra.QuadraticAlgebra.Defs//instructions: +533.3M (+2.48%)