This PR adds high priority to instances for `OfSemiring.Q` in the grind
ring envelope. When Mathlib is imported, instance synthesis for types
like `OfSemiring.Q Nat` becomes very expensive because the solver
explores many irrelevant paths before finding the correct instances. By
marking these instances as high priority and adding shortcut instances
for basic operations (`Add`, `Sub`, `Mul`, `Neg`, `OfNat`, `NatCast`,
`IntCast`, `HPow`), instance synthesis resolves quickly.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Kim Morrison <kim@tqft.net>
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