feat(ModularForm): add eisensteinSeries G_k^v

[WenrongZou]

This PR add the Eisenstein series $G_k^{\bar{v}}$, and prove it as a sum of Eisenstein series $E_k^{\bar{v}}$.

---

[github-actions]

PR summary 766a41c785

Import changes exceeding 2%

%	File
+21.44%	Mathlib.NumberTheory.ModularForms.EisensteinSeries.Basic

Import changes for modified files

Dependency changes

File	Base Count	Head Count	Change
Mathlib.NumberTheory.ModularForms.EisensteinSeries.Basic	2840	3449	+609 (+21.44%)

Import changes for all files

Files	Import difference
12 files Mathlib.NumberTheory.ModularForms.CuspFormSubmodule Mathlib.NumberTheory.ModularForms.DedekindEta Mathlib.NumberTheory.ModularForms.Delta Mathlib.NumberTheory.ModularForms.Derivative Mathlib.NumberTheory.ModularForms.DimensionFormulas.LevelOne Mathlib.NumberTheory.ModularForms.Discriminant Mathlib.NumberTheory.ModularForms.EisensteinSeries.E2.MDifferentiable Mathlib.NumberTheory.ModularForms.EisensteinSeries.E2.Summable Mathlib.NumberTheory.ModularForms.EisensteinSeries.E2.Transform Mathlib.NumberTheory.ModularForms.EisensteinSeries.QExpansion Mathlib.NumberTheory.ModularForms.LevelOne.DimensionFormula Mathlib.NumberTheory.ModularForms.LevelOne.GradedRing	309
Mathlib.NumberTheory.ModularForms.EisensteinSeries.Basic	609

---

Declarations diff (regex)

+ G_eq_sum_E
+ _root_.eisensteinSeriesG
+ bijOn_divIntMap_gammaSet
+ coe_coprimeUnitMap
+ coprimeUnitMap
+ eisSummand_smul
+ eisensteinSeriesGMF
+ eisensteinSeriesGMF_apply
+ eisensteinSeriesMF_apply
+ gammaSetCoprimeSigmaEquiv
+ summable_coprime_eisSummand
+ toCoprimeUnitFiber
+ tsum_gammaSet_eisSummand_of_coprime
+ tsum_zpow_eq_LFunction

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 766a41c).

• +14 new declarations
• −0 removed declarations

+EisensteinSeries.bijOn_divIntMap_gammaSet
+EisensteinSeries.eisSummand_smul
+EisensteinSeries.gammaSetCoprimeSigmaEquiv
+EisensteinSeries.summable_coprime_eisSummand
+G_eq_sum_E
+ModularForm.eisensteinSeriesGMF
+ModularForm.eisensteinSeriesGMF_apply
+ModularForm.eisensteinSeriesMF_apply
+ZMod.coe_coprimeUnitMap
+ZMod.coprimeUnitMap
+eisensteinSeriesG
+toCoprimeUnitFiber
+tsum_gammaSet_eisSummand_of_coprime
+tsum_zpow_eq_LFunction

---

No changes to strong technical debt.

No changes to weak technical debt.

Current commit 766a41c785
Reference commit 052559c5c9

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).

[mathlib-bors]

This pull request is now in draft mode. No active bors state needed cleanup.

While this PR remains draft, bors will ignore commands on this PR. Mark it ready for review before using commands like bors r+ or bors try.