feat(Combinatorics/SimpleGraph): miscellaneous walk lemmas

[pimotte]

Adds some miscellaneous lemmas on walks, in preparation for Tutte's theorem.

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Thread on Tutte

How these lemma's would be used can be found in this commit (marked as In walk_lemmas)

Hopefully the last prequisite PR, after this I expect it all to be the actual proof of Tutte's:D

[github-actions]

PR summary 6130699573

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

+ Connected.one_lt_dist_of_ne_of_not_adj
+ Reachable.one_lt_dist_of_ne_of_not_adj
+ Walk.exists_adj_adj_not_adj_ne
+ connected_induce_supp
+ exists_length_eq_one_iff
+ exists_mem_support_forall_not_adj_toSubgraph_takeUntil
+ reachable_induce_supp

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).

[YaelDillies]

Thanks!

maintainer delegate

[github-actions]

🚀 Pull request has been placed on the maintainer queue by YaelDillies.