Add pyrefly non-exhaustive match as error

[adamtheturtle]

Adds \ to \ in project \ files.

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Note

Low Risk
Config-only change that tightens static analysis; may cause CI failures until code is updated to satisfy the stricter rule.

Overview
Adds a pyrefly configuration block to pyproject.toml that upgrades non-exhaustive-match findings to errors, making incomplete match handling fail the type-check/lint step.

^{Written by Cursor Bugbot for commit 26b9256. This will update automatically on new commits. Configure here.}