Merge bitcoin/bitcoin#34141: miniscript: Use Func and Expr when parsing keys, hashes, and locktimes

4b53cbd692 test: Test for musig() in various miniscript expressions (Ava Chow)
ec0f47b15c miniscript: Using Func and Expr when parsing keys, hashes, and locktimes (Ava Chow)
6fd780d4fb descriptors: Increment key_exp_index in ParsePubkey(Inner) (Ava Chow)
b12281bd86 miniscript: Use a reference to key_exp_index in KeyParser (Ava Chow)
ce4c66eb7c test: Test that key expression indexes match key count (Ava Chow)

Pull request description:

  The miniscript parser currently only looks for the next `)` when parsing key, hash, and locktime expressions. This fails to parse when the expressions contain a nested expression. Currently, this is only possible with `musig()` inside of key expressions. However, this pattern can be generalized to handling hashes and locktimes, so I implemented those too.

  Fixes #34076

ACKs for top commit:
  rkrux:
    ACK 4b53cbd692
  sipa:
    ACK 4b53cbd692
  darosior:
    Other than that, Approach ACK 4b53cbd692. That makes sense to me but i have not closely reviewed the code.

Tree-SHA512: 01040c7b07a59d8e3725ff11ab9543b256aea22535fb94059f490a5bb45319e859666af04c2f0a4edcb8cf1e6dfc7bd8a8271b21ad81143bafccd4d0a39cae9c

src/wallet/test/walletload_tests.cpp

@@ -37,6 +37,8 @@ public:
     std::optional<int64_t> MaxSatisfactionElems() const override { return {}; }
     void GetPubKeys(std::set<CPubKey>& pubkeys, std::set<CExtPubKey>& ext_pubs) const override {}
     std::vector<std::string> Warnings() const override { return {}; }
+    uint32_t GetMaxKeyExpr() const override { return 0; }
+    size_t GetKeyCount() const override { return 0; }
 };
 
 BOOST_FIXTURE_TEST_CASE(wallet_load_descriptors, TestingSetup)