feat: filter out deprecated lemmas from suggestions in exact?/rw?

[kim-em]

This PR filters deprecated lemmas from exact? and rw? suggestions.

Previously, both tactics would suggest deprecated lemmas, which could be confusing for users since using the suggestion would trigger a deprecation warning.

Now, lemmas marked with @[deprecated] are filtered out in the addImport functions that populate the discrimination trees used by these tactics.

Example (before this PR):

import Mathlib.Logic.Basic

example (h : ∃ n : Nat, n > 0) : True := by
  choose (n : Nat) (hn : n > 0 + 0) using h
  guard_hyp hn : n > 0  -- `rw?` would suggest `Eq.rec_eq_cast` which is deprecated

Zulip discussion: https://leanprover.zulipchat.com/#narrow/channel/287929-mathlib4/topic/deprecated.20lemma.20from.20rw.3F/near/554106870

🤖 Prepared with Claude Code

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Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 11e4e44be070ec99bc734e40f8431fd92725842d --onto 0f866236c7c2e77e8d12ff61d08ef48694a0cbfb. You can force Mathlib CI using the force-mathlib-ci label. (2026-01-07 00:34:33)

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• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 11e4e44be070ec99bc734e40f8431fd92725842d --onto 0f866236c7c2e77e8d12ff61d08ef48694a0cbfb. You can force reference manual CI using the force-manual-ci label. (2026-01-07 00:34:34)