feat(NumberTheory/ArithmeticFunction/LFunction): formal Euler products of Dirichlet series

[tb65536]

This PR defines formal Euler products of Dirichlet series. See #36189 for how this will ultimately be used to construct L-functions.

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[github-actions]

PR summary 90795a09a9

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.NumberTheory.ArithmeticFunction.LFunction (new file)	1499

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Declarations diff

+ eulerProduct
+ tendsTo_eulerProduct_of_tendsTo
+ tendsto_iff
+ uniformity_eq

You can run this locally as follows

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

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

The doc-module for scripts/pr_summary/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/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).