feat: define pullback quotient maps

[urkud]

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[github-actions]

PR summary 6955cd00ce

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.Topology.Maps.PullbackQuotient (new file)	758

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Declarations diff

+ ClusterPt.nhds_inf
+ Continuous.pullbackFst
+ Continuous.pullbackSnd
+ Equiv.pullbackProdFst
+ Fin.insertNthHomeomorph
+ Homeomorph.piOptionHomeomorphProd
+ Homeomorph.pullbackProdFst
+ TopologicalSpace.IsTopologicalBasis.isPullbackQuotientMap_iff
+ Topology.IsPullbackQuotientMap
+ _root_.Homeomorph.isPullbackQuotientMap
+ _root_.IsOpenQuotientMap.isPullbackQuotientMap
+ clusterPt_nhds_inf
+ comp
+ exists_finite_subset_biUnion_image_mem_nhds
+ exists_finset_biUnion_image_mem_nhds
+ id
+ isPullbackQuotientMap_iff_exists_finite_image_mem_nhds
+ isQuotientMap
+ of_forall_pullback
+ of_forall_pullback_nhdsAdjoint
+ of_isEmpty
+ of_subsingleton
+ piMap
+ prodMap
+ prodSwap
+ pullback
+ surjective

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).