feat(crypto): add Zcash ZIP-243 sighash implementation

Add support for Zcash transaction signature validation following ZIP-243
standard. The implementation uses BLAKE2b-256 with personalization strings
for computing signature hashes for transparent inputs in Zcash transactions.

Key features:
- Implement ZIP-243 sighash algorithm for Zcash transactions
- Add SighashCacheZcashExt trait for computing Zcash sighashes
- Support both P2PKH and P2SH inputs in Zcash transparent transactions
- Provide PSBT signing extension for Zcash inputs
- Include test vectors from ZIP-243 specification

Issue: BTC-2555

Co-authored-by: llm-git <[email protected]>

Author: OttoAllmendinger

altcoins/zcash/ZIP-243-TEST-VECTORS.md

@@ -0,0 +1,118 @@
+# ZIP-243 Test Vectors
+
+Source: https://zips.z.cash/zip-0243
+
+## Test Vector 1 (Shielded-only, no transparent inputs)
+
+This transaction has NO transparent inputs (vin: 00), so it's not useful for testing
+transparent sighash computation.
+
+**Expected sighash** (with nIn = NOT_AN_INPUT, SIGHASH_ALL): `63d18534de5f2d1c9e169b73f9c783718adbef5c8a7d55b5e7a37affa1dd3ff3`
+
+---
+
+## Test Vector 2 (Mixed: 2 transparent inputs + shielded outputs)
+
+**Transaction Header:**
+- header: `04000080`
+- nVersionGroupId: `85202f89` 
+- nLockTime: `d7034302` (0x020343d7 = 33866711)
+- nExpiryHeight: `011b9a07` (0x079a1b01 = 127671041)
+- valueBalance: `6620edc067ff0200`
+
+**Transparent Inputs (vin: 02):**
+1. Input 0:
+   - txid: `0bbe32a598c22adfb48cef72ba5d4287c0cefbacfd8ce195b4963c34a94bba7a`
+   - vout: `175dae4b` (little-endian: 0x4bae5d17)
+   - scriptSig: `0465ac6563`
+   - nSequence: `53708915`
+
+2. Input 1:
+   - txid: `090f47a068e227433f9e49d3aa09e356d8d66d0c0121e91a3c4aa3f27fa1b633`
+   - vout: `96e2b41d` (little-endian: 0x1db4e296)
+   - scriptSig: `090063535300ac53ac51`
+   - nSequence: `4e970568`
+
+**Expected values (nIn = 0, SIGHASH_NONE = 2):**
+- hashPrevouts: `cacf0f5210cce5fa65a59f314292b3111d299e7d9d582753cf61e1e408552ae4`
+- hashSequence: zeros (due to SIGHASH_NONE)
+- hashOutputs: zeros (due to SIGHASH_NONE)
+- **sighash**: `bbe6d84f57c56b29b914c694baaccb891297e961de3eb46c68e3c89c47b1a1db`
+
+---
+
+## Test Vector 3 (Transparent-only) ⭐ BEST FOR TESTING
+
+**Testnet transaction** with txid `97d8814886d07fc12bbac90c089a10f90906cbb53402ee26e576ef99276c492d`
+
+This is a **transparent-only** transaction (no shielded components), perfect for testing.
+
+**Raw Transaction:**
+```
+0400008085202f8901a8c685478265f4c14dada651969c45a65e1aeb8cd6791f2f5bb6a1d9952104d9010000006b483045022100a61e5d557568c2ddc1d9b03a7173c6ce7c996c4daecab007ac8f34bee01e6b9702204d38fdc0bcf2728a69fde78462a10fb45a9baa27873e6a5fc45fb5c76764202a01210365ffea3efa3908918a8b8627724af852fc9b86d7375b103ab0543cf418bcaa7ffeffffff02005a6202000000001976a9148132712c3ff19f3a151234616777420a6d7ef22688ac8b959800000000001976a9145453e4698f02a38abdaa521cd1ff2dee6fac187188ac29b0040048b004000000000000000000000000
+```
+
+**Transaction Fields:**
+- header: `04000080` (version 4 with fOverwintered)
+- nVersionGroupId: `85202f89` (Sapling)
+- nLockTime: `29b00400` = 307241 (little-endian: 0x0004b029)
+- nExpiryHeight: `48b00400` = 307272 (little-endian: 0x0004b048)
+- valueBalance: `0000000000000000` (zeros for transparent-only)
+
+**Transparent Input (vin: 01):**
+- txid: `a8c685478265f4c14dada651969c45a65e1aeb8cd6791f2f5bb6a1d9952104d9`
+- vout: `01000000` = 1
+- scriptSig (signed): `6b483045022100a61e5d557568c2ddc1d9b03a7173c6ce7c996c4daecab007ac8f34bee01e6b9702204d38fdc0bcf2728a69fde78462a10fb45a9baa27873e6a5fc45fb5c76764202a01210365ffea3efa3908918a8b8627724af852fc9b86d7375b103ab0543cf418bcaa7f`
+- nSequence: `feffffff` = 4294967294 (0xfffffffe)
+
+**Transparent Outputs (vout: 02):**
+1. Output 0:
+   - value: `005a620200000000` = 40000000 satoshis (0.4 ZEC)
+   - scriptPubKey: `1976a9148132712c3ff19f3a151234616777420a6d7ef22688ac`
+
+2. Output 1:
+   - value: `8b95980000000000` = 9999755 satoshis
+   - scriptPubKey: `1976a9145453e4698f02a38abdaa521cd1ff2dee6fac187188ac`
+
+**Sighash Input Data (for computing sighash of input 0):**
+- prevout txid: `a8c685478265f4c14dada651969c45a65e1aeb8cd6791f2f5bb6a1d9952104d9`
+- prevout vout: `01000000` = 1
+- scriptCode: `1976a914507173527b4c3318a2aecd793bf1cfed705950cf88ac` (P2PKH)
+- amount: `80f0fa0200000000` = 50000000 satoshis (0.5 ZEC)
+- nSequence: `feffffff`
+
+**Intermediate Hashes (SIGHASH_ALL):**
+- hashPrevouts: `fae31b8dec7b0b77e2c8d6b6eb0e7e4e55abc6574c26dd44464d9408a8e33f11`
+- hashSequence: `6c80d37f12d89b6f17ff198723e7db1247c4811d1a695d74d930f99e98418790`
+- hashOutputs: `d2b04118469b7810a0d1cc59568320aad25a84f407ecac40b4f605a4e6868454`
+- hashJoinSplits: zeros
+- hashShieldedSpends: zeros
+- hashShieldedOutputs: zeros
+
+**Expected Sighash (nIn = 0, SIGHASH_ALL = 1):**
+```
+f3148f80dfab5e573d5edfe7a850f5fd39234f80b5429d3a57edcc11e34c585b
+```
+
+---
+
+## Consensus Branch IDs
+
+| Network Upgrade | Branch ID    | Transaction Version |
+|-----------------|--------------|---------------------|
+| Overwinter      | 0x5ba81b19   | 3                   |
+| Sapling         | 0x76b809bb   | 4                   |
+| Blossom         | 0x2bb40e60   | 4                   |
+| Heartwood       | 0xf5b9230b   | 4                   |
+| Canopy          | 0xe9ff75a6   | 4                   |
+| NU5             | 0xc2d6d0b4   | 5                   |
+
+## Personalization Strings
+
+| Purpose  | Personalization (16 bytes)   |
+|----------|------------------------------|
+| Sighash  | "ZcashSigHash" + branch_id   |
+| Prevouts | "ZcashPrevoutHash"           |
+| Sequence | "ZcashSequencHash"           |
+| Outputs  | "ZcashOutputsHash"           |
+