chore: Use old poseidon wrapper for tree operations on v1 registry

[Kemperino]

contract size: 21,242

	public	internal	linked tree + internal
fs update leaf 0	427,473	395,557 (-7.5%)	399,194(-6.6%)
fs update leaf 500	427,574	395,658 (-7.5%)	399,248 (-6.6%)
fs update leaf 999	423,458	391,542 (-7.5%)	395,132 (-6.7%)

❯ jq '.bytecode.linkReferences' out/WorldIDRegistryV2Unreleased.sol/WorldIDRegistryV2.json
{
  "src/core/libraries/FullStorageBinaryIMT.sol": {
    "FullStorageBinaryIMT": [
      {
        "start": 2417,
        "length": 20
      },
      {
        "start": 5885,
        "length": 20
      },
      {
        "start": 10505,
        "length": 20
      },
      {
        "start": 17188,
        "length": 20
      }
    ]
  },
  "src/core/libraries/PackedAccountData.sol": {
    "PackedAccountData": [
      {
        "start": 4339,
        "length": 20
      },
      {
        "start": 7714,
        "length": 20
      },
      {
        "start": 11454,
        "length": 20
      },
      {
        "start": 12630,
        "length": 20
      },
      {
        "start": 13664,
        "length": 20
      },
      {
        "start": 15887,
        "length": 20
      },
      {
        "start": 16808,
        "length": 20
      },
      {
        "start": 17402,
        "length": 20
      }
    ]
  }
}

Note

Medium Risk
Changes how Merkle roots are computed on V1 write paths; a mismatch with deployed behavior would break proof validity, though the intent is bytecode-level compatibility with the original public Poseidon call pattern.

Overview
Splits V1 registry Merkle writes from the shared FullStorageBinaryIMT helpers so they always hash through a V1-style public Poseidon2T2V1 library call, matching how the original registry built roots.

WorldIDRegistry now routes insert/update/batch insert via virtual _insertLeaf, _insertManyLeaves, and _updateLeafAndRecord that delegate to new WorldIDRegistryV1Tree (logic copied from the IMT library, using Poseidon2T2V1). FullStorageBinaryIMT widens _key / _getNode to internal so that library can reuse node lookups. WorldIDRegistryV2 overrides those hooks to keep using FullStorageBinaryIMT with the current internal Poseidon2T2 path for post-upgrade behavior.

^{Reviewed by Cursor Bugbot for commit 9339ab4. Configure here.}