feat(RingTheory): more algebra instances for HomogeneousLocalization and linear constructors

[kckennylau]

This PR introduces the instance Algebra R₀ (HomogeneousLocalization 𝒜 x) as well as two linear constructors mkₗ and Away.mkₗ that fix the denominator.

Zulip discussion: #mathlib4 > Some algebra instance for graded algebra and homog loc

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Split from #26061.

[github-actions]

PR summary e978dd5d9f

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

+ Away.mkₗ
+ Away.mkₗ_apply
+ algebraMap_apply'
+ instance : Algebra R₀ (HomogeneousLocalization 𝒜 x)
+ instance : IsScalarTower R (𝒜 0) (HomogeneousLocalization 𝒜 x)
+ instance : IsScalarTower R₀ R (HomogeneousLocalization 𝒜 x)
+ mkₗ
+ val_fromZeroRingHom

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

The doc-module for script/declarations_diff.sh contains some details about this script.

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No changes to technical debt.

You can run this locally as

./scripts/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).