feat(Order/Monoid/Unbundled): make mulLeftMono_of_mulLeftStrictMono and mulRightMono_of_mulRightStrictMono instances.

[homeowmorphism]

In response to feedback on #41505 (comment).

---

[github-actions]

PR summary dc3116dcc4

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 dc3116dcc4
Reference commit 4d6f98930f

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).

[github-actions]

🚨 PR Title Needs Formatting

Please update the title to match our commit style conventions.

Errors from script:

labels are []
error: the PR title should not end with a full stop

Details on the required title format

The title should fit the following format:

<kind>(<optional-scope>): <subject>

<kind> is:

• feat (feature)
• fix (bug fix)
• doc (documentation)
• style (formatting, missing semicolons, ...)
• refactor
• test (when adding missing tests)
• chore (maintain)
• perf (performance improvement, optimization, ...)
• ci (changes to continuous integration, repo automation, ...)

<optional-scope> is a name of module or a directory which contains changed modules.
This is not necessary to include, but may be useful if the <subject> is insufficient.
The Mathlib directory prefix is always omitted.
For instance, it could be

• Data/Nat/Basic
• Algebra/Group/Defs
• Topology/Constructions

<subject> has the following constraints:

• do not capitalize the first letter
• no dot(.) at the end
• use imperative, present tense: "change" not "changed" nor "changes"

[homeowmorphism]

One thing that came to my attention after discussing with Claude is that this change may create an instance loop because we have

instance mulLeftMono_of_mulLeftStrictMono (M) [Mul M] [PartialOrder M] [MulLeftStrictMono M] :
    MulLeftMono M := covariantClass_le_of_lt _ _ _

and

instance IsLeftCancelMul.mulLeftStrictMono_of_mulLeftMono [Mul N] [IsLeftCancelMul N]
    [PartialOrder N] [MulLeftMono N] :
    MulLeftStrictMono N

and this may waste heartbeats.

Not sure if it matters in the big picture. I made a gist report in case someone more knowledgeable than myself wants to have a look: https://gist.github.com/homeowmorphism/5d1f1f699df9a448dedecd2643b2f737.