Add NATIVE_DECIMALS & solana constants #872

Job	Run time
lint	1m 7s
tests (tests/integration/test_async_http_client.py)	1m 7s
tests (tests/integration/test_async_token_client.py)	1m 21s
tests (tests/integration/test_http_client.py)	1m 14s
tests (tests/integration/test_token_client.py)	1m 14s
tests (tests/integration/test_websockets.py)	2m 25s
tests (tests/integration/test_recent_performance_samples.py)	2m 1s
tests (tests/integration/test_memo.py)	1m 13s
tests (tests/unit)	31s
tests (src)	29s
coverage	29s
test	1s
	13m 12s

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