Wire Taproot script verification into validation/policy/libconsensus and update standardness flags.
Adapt wallet_multiwallet functional test to match filesystem error variants (create_directory/create_directories/filesystem error), making the suite robust across fs backends and library versions.
- use Bech32 for witness v0 and Bech32m for witness v1+ in key_io
- update C++ bech32 tests and python segwit_addr framework
- realign key/address test vectors and fixtures to Palladium prefixes/params
- adjust chain-parameter-sensitive tests (maturity, BIP66/regtest, message verify)
- fix incorrect historical sha256 expected vector in unit tests
Update all references to 'testnet3' to 'testnet' for consistency. This includes:
- Changing magic bytes in network messages
- Updating directory paths and configuration files
- Modifying documentation and test framework references
- Adjusting chain parameters and validation logic
