feat(NumberTheory/RamificationInertia/Unramified): generalize IsUnramifiedAt.of_liesOver to flat algebras

[tb65536]

This PR generalizes IsUnramifiedAt.of_liesOver to flat algebras and deprecates the technical auxiliary lemma IsUnramifiedAt.of_liesOver_of_ne_bot for the previous proof.

This also avoids the usage of the old Ideal.ramificationIdx'.

---

[github-actions]

PR summary cc790ce8a4

Import changes for modified files

Dependency changes

File	Base Count	Head Count	Change
Mathlib.RingTheory.Flat.FaithfullyFlat.Algebra	1737	1741	+4 (+0.23%)

Import changes for all files

Files	Import difference
3 files Mathlib.RingTheory.Flat.FaithfullyFlat.Algebra Mathlib.RingTheory.LocalRing.Length Mathlib.RingTheory.TensorProduct.IncludeLeftSubRight	4

---

Declarations diff (regex)

+ IsUnramifiedAt.map_eq
+ instance [Module.Flat A B] (p : Ideal A) (q : Ideal B) [p.IsPrime] [q.IsPrime] [q.LiesOver p]

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 cc790ce).

• +2 new declarations
• −0 removed declarations

+Algebra.IsUnramifiedAt.map_eq
+instFaithfullyFlatAtPrimeOfFlatOfIsLiesOverAlgebra

---

No changes to strong technical debt.

No changes to weak technical debt.

Current commit cc790ce8a4
Reference commit b948c053cf

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).