Add NATIVE_DECIMALS & solana constants #871

Job	Run time
lint	1m 8s
tests (tests/integration/test_async_http_client.py)	1m 14s
tests (tests/integration/test_async_token_client.py)	1m 10s
tests (tests/integration/test_http_client.py)	1m 9s
tests (tests/integration/test_token_client.py)	1m 16s
tests (tests/integration/test_websockets.py)	2m 26s
tests (tests/integration/test_recent_performance_samples.py)	2m 0s
tests (tests/integration/test_memo.py)	1m 19s
tests (tests/unit)	26s
tests (src)	35s
coverage	39s
test	1s
	13m 23s

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