feat(Data/Real/EReal): add mul_lt_mul_of_pos_left theorem

[dobronx1325]

This PR adds the theorem EReal.mul_lt_mul_of_pos_left, which states that for a positive real number a and extended reals b < c, left multiplication by a preserves the strict order: (a : EReal) * b < (a : EReal) * c.

The theorem complements existing order-preserving properties for addition in EReal and extends the algebraic structure for multiplication. The proof uses basic properties of extended reals and order relations.

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[github-actions]

PR summary 1e783fb5e4

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

+ mul_lt_mul_of_pos_left

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).