feat: haveI/letI tactic linter

[JovanGerb]

This PR implements a variation on the linter that was written by Claude in #41562. It suggest to use have/let instead of haveI/letI whenever the goal is a proposition.

See also https://leanprover.zulipchat.com/#narrow/channel/287929-mathlib4/topic/surprising.20have.2FhaveI.20kernel.20phenomenon/with/609718493

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[github-actions]

PR summary 2197c33724

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
../mathlib-ci/scripts/pr_summary/import_trans_difference.sh all
There are 8208 files with changed transitive imports taking up over 357980 characters: this is too many to display!
You can run this locally from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

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Declarations diff (regex)

+ runHaveI
+ runLetI

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 2197c33).

• +3 new declarations
• −0 removed declarations

+Mathlib.Linter.HaveILetI.linter.style.haveILetI
+Mathlib.Linter.HaveILetI.tacticHaveI__
+Mathlib.Linter.HaveILetI.tacticLetI__

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No changes to strong technical debt.

No changes to weak technical debt.

Current commit 2197c33724
Reference commit f98b1aa39a

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).

[Vierkantor]

This looks good to me: although there was the suggestion to merge this with the let-for-Prop linter, it seems there is no obvious way to merge the two implementations (apart from putting them in the same file maybe?). The implementation is a lot neater than my idea of digging around in infotrees with TacticAnalysis :)

I'll wait with delegating until everything builds and @thorimur has had a chance to comment.