v4.27.0

[pandaman64]

Note

Upgrade to Lean v4.27.0

• Updates lean-toolchain to v4.27.0 for correctness, docbuild, and regex
• Refreshes lake-manifest.json and lakefile.toml pins: mathlib to v4.27.0 and newer SHAs for proofwidgets, aesop, Qq, batteries, plausible, LeanSearchClient, importGraph, Cli, doc-gen4, etc.

Minor proof maintenance

• In RegexCorrectness/Backtracker/Basic.lean, add rfl after rw! [pushNext, ...] in several pushNext case lemmas (done, fail, epsilon, split, saveFin, save) to close equalities.

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