db: unify everything to use big-endian encoding, not mixed

Performance-wise, LE was a tiny bit faster though not consistently.
Perf goes 3-4% both ways, twice in LE's favour, once in BE's favour.

Still, BE is nicer as that's the natural order for leveldb comparators.

```
$ python3 -m timeit -n1 -r10 --setup "import random; from electrumx.lib.util import unpack_be_uint64, unpack_le_uint64; arr = [random.randbytes(8) for _ in range(10**7)]" "[unpack_be_uint64(x) for x in arr]"
1 loop, best of 10: 1.12 sec per loop

$ python3 -m timeit -n1 -r10 --setup "import random; from electrumx.lib.util import unpack_be_uint64, unpack_le_uint64; arr = [random.randbytes(8) for _ in range(10**7)]" "[unpack_le_uint64(x) for x in arr]"
1 loop, best of 10: 1.08 sec per loop

$ python3 -m timeit -n1 -r10 --setup "import random; from electrumx.lib.util import pack_be_uint64, pack_le_uint64; arr = [int.from_bytes(random.randbytes(8), byteorder='big') for _ in range(10**7)]" "[pack_be_uint64(x) for x in arr]"
1 loop, best of 10: 683 msec per loop

$ python3 -m timeit -n1 -r10 --setup "import random; from electrumx.lib.util import pack_be_uint64, pack_le_uint64; arr = [int.from_bytes(random.randbytes(8), byteorder='big') for _ in range(10**7)]" "[pack_le_uint64(x) for x in arr]"
1 loop, best of 10: 705 msec per loop
```

```
$ python3 -m timeit -n1 -r10 --setup "import random; from electrumx.lib.util import unpack_be_uint32, unpack_le_uint32; arr = [random.randbytes(4) for _ in range(10**7)]" "[unpack_be_uint32(x) for x in arr]"
1 loop, best of 10: 1.03 sec per loop

$ python3 -m timeit -n1 -r10 --setup "import random; from electrumx.lib.util import unpack_be_uint32, unpack_le_uint32; arr = [random.randbytes(4) for _ in range(10**7)]" "[unpack_le_uint32(x) for x in arr]"
1 loop, best of 10: 1.03 sec per loop

$ python3 -m timeit -n1 -r10 --setup "import random; from electrumx.lib.util import pack_be_uint32, pack_le_uint32; arr = [int.from_bytes(random.randbytes(4), byteorder='big') for _ in range(10**7)]" "[pack_be_uint32(x) for x in arr]"
1 loop, best of 10: 629 msec per loop

$ python3 -m timeit -n1 -r10 --setup "import random; from electrumx.lib.util import pack_be_uint32, pack_le_uint32; arr = [int.from_bytes(random.randbytes(4), byteorder='big') for _ in range(10**7)]" "[pack_le_uint32(x) for x in arr]"
1 loop, best of 10: 605 msec per loop
```

Author: SomberNight

src/electrumx/server/db.py

@@ -76,7 +76,7 @@ class DB:
     it was shutdown uncleanly.
     '''
 
-    DB_VERSIONS = (10, )
+    DB_VERSIONS = (11, )
     DB_STATE_KEY = b'state'
 
     utxo_db: Optional['Storage']

src/electrumx/server/db_util.py

@@ -5,8 +5,6 @@
 from typing import Sequence
 
 from electrumx.lib.util import (
-    pack_le_uint32, unpack_le_uint32,
-    pack_le_uint64, unpack_le_uint64,
     pack_be_uint32, unpack_be_uint32,
     pack_be_uint64, unpack_be_uint64,
 )
@@ -25,26 +23,34 @@ def pack_txnum(tx_num: int) -> bytes:
     return pack_be_uint64(tx_num)[-TXNUM_LEN:]
 
 
+assert pack_txnum(0x123) == bytes.fromhex("0000000123")
+assert unpack_txnum(pack_txnum(0x123)) == 0x123
+
+
 # txout_idx
 TXOUTIDX_LEN = 3
 TXOUTIDX_PADDING = bytes(4 - TXOUTIDX_LEN)
 
 
 def unpack_txoutidx(txout_idx: bytes) -> int:
-    return unpack_le_uint32(txout_idx + TXOUTIDX_PADDING)[0]
+    return unpack_be_uint32(TXOUTIDX_PADDING + txout_idx)[0]
 
 
 def pack_txoutidx(txout_idx: int) -> bytes:
-    return pack_le_uint32(txout_idx)[:TXOUTIDX_LEN]
+    return pack_be_uint32(txout_idx)[-TXOUTIDX_LEN:]
+
+
+assert pack_txoutidx(0x123) == bytes.fromhex("000123")
+assert unpack_txoutidx(pack_txoutidx(0x123)) == 0x123
 
 
 # sats
 def unpack_satoshis_val(sats: bytes) -> int:
-    return unpack_le_uint64(sats)[0]
+    return unpack_be_uint64(sats)[0]
 
 
 def pack_satoshis_val(sats: int) -> bytes:
-    return pack_le_uint64(sats)
+    return pack_be_uint64(sats)
 
 
 # block height
@@ -64,11 +70,11 @@ def pack_block_height(bheight: int) -> bytes:
 
 
 def unpack_dyn_header_offset(offset: bytes) -> int:
-    return unpack_le_uint64(offset)[0]
+    return unpack_be_uint64(offset)[0]
 
 
 def pack_dyn_header_offset(offset: int) -> bytes:
-    return pack_le_uint64(offset)
+    return pack_be_uint64(offset)
 
 
 class DBTooOldForMigrations(RuntimeError):