feat(by_contra,contrapose): warn if the push_neg step does nothing

[grunweg]

---

• depends on: [Merged by Bors] - refactor(Tactic/Util/AtLocation): allow throwing a warning when no progress is being made #31597
• depends on: refactor(AtLocation): allow throwing a warning when no progress is being made #37899
• depends on: [Merged by Bors] - chore: avoid superfluous use of push_neg with contrapose, by_contra o… #37937
• depends on: [Merged by Bors] - chore(AtLocation): clean up backtick handling #37999
• depends on: [Merged by Bors] - feat(push): error message tweaks #38008
• depends on: chore: prefer contrapose over contrapose!, when possible #43999

[github-actions]

PR summary 246f1e82ea

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff (regex)

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

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 -- pending)

Computed after the build finishes.

---

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

Current commit 246f1e82ea
Reference commit b1007d8abf

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).

[mathlib-merge-conflicts]

This pull request has conflicts, please merge master and resolve them.

[mathlib-dependent-issues]

This PR/issue depends on:

• [Merged by Bors] - refactor(Tactic/Util/AtLocation): allow throwing a warning when no progress is being made #31597
• refactor(AtLocation): allow throwing a warning when no progress is being made #37899
• [Merged by Bors] - chore: avoid superfluous use of push_neg with contrapose, by_contra o… #37937
• [Merged by Bors] - chore(AtLocation): clean up backtick handling #37999
• [Merged by Bors] - feat(push): error message tweaks #38008
• chore: prefer contrapose over contrapose!, when possible #43999
  By Dependent Issues (🤖). Happy coding!

[grunweg]

The remaining two warnings on the archive are false positives...

[mathlib-merge-conflicts]

This pull request has conflicts, please merge master and resolve them.