Fix verify_proof host functions for Substrate compact proofs

[x3c41a]

Fixes the implementation of ext_trie_blake2_256_verify_proof_version_1 and _version_2 added in #2221. That PR used proof_decode::decode_and_verify_proof, which expects regular Merkle proofs where every node is fully encoded and looked up by its blake2b hash. Substrate generates compact proofs via sp_trie::generate_trie_proof (trie-db's generate_proof): along the proven path, child references are replaced by an empty inline placeholder and the actual child nodes follow as the next proof entries; the target leaf's value is also omitted and reconstructed from the caller-supplied expected value (hashed if state version V1 and >= 32 bytes).

What this PR does

Adds verify_compact_trie_proof in trie::proof_decode and wires the two host functions to it. The verifier:

1. SCALE-decodes the proof into a stream of node entries.
2. Reads the first entry as the root node; decodes it.
3. Matches the partial key prefix, then descends one nibble at a time:
   • If the child reference is an empty inline placeholder, consumes the next proof entry as that child's node and recurses.
   • If the child reference is an inline non-empty node, decodes it directly without consuming a proof entry.
   • If the child reference is a 32-byte hash, returns false (descending into a non-path child means the proof is incomplete for this key).
4. At the target node, injects the caller-supplied value (as Unhashed or Hashed(blake2b(value)) based on state version and value length).
5. Re-encodes the node with the reconstructed children/value and computes its merkle value.
6. Returns true iff the final root node's hash equals the caller-supplied root.

Tests

Seven unit tests in trie::proof_decode::tests cover the verifier using proof bytes captured live from paseo-bulletin-rpc.polkadot.io block #1503870 (a 256-byte chunk-trie proof from pallet-transaction-storage's apply_block_inherents):

• verify_compact_proof_accepts_valid_substrate_proof — positive case.
• verify_compact_proof_rejects_wrong_root — flipping a bit in the root.
• verify_compact_proof_rejects_wrong_value — flipping a bit in the value.
• verify_compact_proof_rejects_wrong_key — different key.
• verify_compact_proof_rejects_wrong_state_version — V0 instead of V1.
• verify_compact_proof_rejects_tampered_proof_byte — corrupted byte inside the root node entry.
• verify_compact_proof_rejects_truncated_proof — missing the leaf entry.

End-to-end, replaying five real ProofChecked-emitting blocks (1503870, 1504069, 1504256, 1504290, 1504307, 1504375) through chopsticks run-block against paseo-bulletin now completes finalize_block without panicking on the Storage proof must be checked once in the block assertion. Previously, with #2221's implementation, all of them panicked.

Ref: paritytech/polkadot-bulletin-chain#341

[x3c41a]

Closing — re-opening against the active upstream paritytech/smoldot, which is where new development happens. This repo (smoldot-archive) is the older fork and chopsticks pulls from it via the smol-dot/smoldot redirect, but the host function fix should land in the active fork first.