This PR adds support for `try?` to use induction; it will only perform
induction on inductive types defined in the current namespace and/or
module; so in particular for now it will not induct on built-in
inductives such as `Nat` or `List`.
This is stacked on top of #11132, and there are overlapping changes.
<!-- CURSOR_SUMMARY -->
---
> [!NOTE]
> Adds vanilla induction suggestions to `try?`, updates collection of
inductive candidates, and tests the new behavior on custom inductive
types.
>
> - **Try tactic pipeline**:
> - Add vanilla induction generators (`mkIndStx`, `mkAllIndStx`) that
try `induction <var> <;> …`, with fallback via `expose_names` when
needed.
> - Integrate induction into `mkTryEvalSuggestStx`, alongside existing
atomic, suggestions, and function-induction options.
> - **Collector updates (`Try/Collect.lean`)**:
> - Enhance `checkInductive` to `whnf` the type and use `getAppFn` to
detect inductive heads, populating `indCandidates`.
> - **Tests**:
> - New `tests/lean/run/try_induction.lean` covering suggestions for
`induction` on custom inductives, interaction with `grind`, and
coexistence with `fun_induction`.
>
> <sup>Written by [Cursor
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b357990c97d0855418202626dad3a73cdcae8a86. This will update automatically
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<!-- /CURSOR_SUMMARY -->
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Co-authored-by: Claude <noreply@anthropic.com>
d1e19f2aa0