fix: use correct leafVersion in control block byte for non-default version leaves

[jasonandjay]

Summary

Fix the first byte of scriptPathControlBlocks[1] in the p2mr_different_version_leaves
test vector. The control block incorrectly uses 0xC1 (leafVersion 192) instead of 0xFB
(leafVersion 250) for a leaf explicitly declared with "leafVersion": 250.

Problem

The P2MR control block's first byte encodes both the leaf version and parity bit:

controlBlock[0] = (leafVersion & 0xfe) | parityBit

For P2MR, the parity bit is always 1. So:

• leafVersion 192 (0xC0) → 0xC1
• leafVersion 250 (0xFA) → 0xFB

The test vector defines two leaves:

{ "id": 0, "leafVersion": 192, "script": "...OP_CHECKSIG" }
{ "id": 1, "leafVersion": 250, "script": "06424950333431" }

But the current control block for leaf1 starts with 0xC1:

scriptPathControlBlocks[1] = "c1 8ad69ec7cf41c2a4001fd1f738bf1e505ce2277acdcaa63fe4765192497f47a7"
                               ^^
                               0xC1 → leafVersion = 0xC0 = 192  ✗ (should be 250)

This is incorrect because a verifier would extract leafVersion = 0xC1 & 0xFE = 0xC0 = 192
from this byte, then compute tapleafHash(script, version=192) which produces a
completely different hash than the correct tapleafHash(script, version=250), making
it impossible to reconstruct the correct Merkle root.

Fix

Change the first byte from 0xC1 to 0xFB:

scriptPathControlBlocks[1] = "fb 8ad69ec7cf41c2a4001fd1f738bf1e505ce2277acdcaa63fe4765192497f47a7"
                               ^^
                               0xFB → leafVersion = 0xFA = 250  ✓

Verification:

tapleafHash(script="06424950333431", version=250) = f224a923cd0021ab202ab139cc56802ddb92dcfc172b9212261a539df79a112a
sibling = leafHash[0] = 8ad69ec7cf41c2a4001fd1f738bf1e505ce2277acdcaa63fe4765192497f47a7

tapBranchHash(f224a923..., 8ad69ec7...) → hashes are sorted internally
→ 6c2dc106ab816b73f9d07e3cd1ef2c8c1256f519748e0813e4edd2405d277bef = merkleRoot ✓

Changes

• p2mr_different_version_leaves: change scriptPathControlBlocks[1] first byte from c1 to fb