Only use v14 decoding for events

[thewhaleking]

For events, the Python is the same speed at decoding as bt-decode (sometimes faster). However, the Python scalecodec offers significantly better decoding, and doesn't rely on us hacking it after the fact.

Compare the following.
bt-decode

{'phase': 'ApplyExtrinsic', 'extrinsic_idx': 1, 'event': {'module_id': 'SubtensorModule', 'event_id': 'CRV3WeightsCommitted', 'attributes': (((174, 102, 210, 111, 237, 83, 159, 197, 1, 180, 52, 15, 170, 239, 101, 226, 15, 235, 13, 191, 56, 134, 88, 153, 124, 3, 75, 171, 173, 6, 191, 67),), 30, ((166, 180, 229, 200, 36, 29, 96, 236, 224, 194, 80, 86, 177, 159, 125, 33, 174, 132, 82, 105, 252, 119, 26, 212, 107, 243, 224, 17, 134, 81, 41, 165),))}, 'topics': []}

scalecodec:

{'phase': 'ApplyExtrinsic', 'extrinsic_idx': 1, 'event': {'event_index': '0759', 'module_id': 'SubtensorModule', 'event_id': 'CRV3WeightsCommitted', 'attributes': ('5G1NjW9YhXLadMWajvTkfcJy6up3yH2q1YzMXDTi6ijanChe', 30, '0xa6b4e5c8241d60ece0c25056b19f7d21ae845269fc771ad46bf3e011865129a5')}, 'event_index': 7, 'module_id': 'SubtensorModule', 'event_id': 'CRV3WeightsCommitted', 'attributes': ('5G1NjW9YhXLadMWajvTkfcJy6up3yH2q1YzMXDTi6ijanChe', 30, '0xa6b4e5c8241d60ece0c25056b19f7d21ae845269fc771ad46bf3e011865129a5'), 'topics': []}

The bt-decode version does not decode the SS58s. In addition, we'd previously had to use various hacks to get inner values to parse correctly:

async-substrate-interface/async_substrate_interface/async_substrate.py

Lines 1933 to 1939 in 35728ab

	if isinstance(value, dict):
	# Convert nested single-key dictionaries to their keys as strings
	for sub_key, sub_value in value.items():
	if isinstance(sub_value, dict):
	for sub_sub_key, sub_sub_value in sub_value.items():
	if sub_sub_value == ():
	attributes[key][sub_key] = sub_sub_key

which changes {"pays_fee": {"Yes": ()}} to {"pays_fee": "Yes"}

This rectifies these issues by just using the MetadataV14 decoder.