bitcoin.py/transaction.py: API changes: rm most hex usage

Instead of some functions operating with hex strings,
and others using bytes, this consolidates most things to use bytes.

This mainly focuses on bitcoin.py and transaction.py,
and then adapts the API usages in other files.

Notably,
- scripts,
- pubkeys,
- signatures
should be bytes in almost all places now.

electrum/bip32.py

@@ -11,7 +11,7 @@ from .util import bfh, BitcoinException
 from . import constants
 from . import ecc
 from .crypto import hash_160, hmac_oneshot
-from .bitcoin import rev_hex, int_to_hex, EncodeBase58Check, DecodeBase58Check
+from .bitcoin import EncodeBase58Check, DecodeBase58Check
 from .logging import get_logger
 
 
@@ -49,7 +49,7 @@ def CKD_priv(parent_privkey: bytes, parent_chaincode: bytes, child_index: int) -
     is_hardened_child = bool(child_index & BIP32_PRIME)
     return _CKD_priv(parent_privkey=parent_privkey,
                      parent_chaincode=parent_chaincode,
-                     child_index=bfh(rev_hex(int_to_hex(child_index, 4))),
+                     child_index=int.to_bytes(child_index, length=4, byteorder="big", signed=False),
                      is_hardened_child=is_hardened_child)
 
 
@@ -85,7 +85,7 @@ def CKD_pub(parent_pubkey: bytes, parent_chaincode: bytes, child_index: int) ->
     if child_index & BIP32_PRIME: raise Exception('not possible to derive hardened child from parent pubkey')
     return _CKD_pub(parent_pubkey=parent_pubkey,
                     parent_chaincode=parent_chaincode,
-                    child_index=bfh(rev_hex(int_to_hex(child_index, 4))))
+                    child_index=int.to_bytes(child_index, length=4, byteorder="big", signed=False))
 
 
 # helper function, callable with arbitrary 'child_index' byte-string.