Add NATIVE_DECIMALS & LAMPORTS_PER_SOL constants #866

Job	Run time
tests (tests/integration/test_async_http_client.py)	1m 12s
lint	29s
tests (tests/integration/test_async_token_client.py)	1m 13s
tests (tests/integration/test_http_client.py)	1m 13s
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 2s
tests (tests/integration/test_memo.py)	1m 24s
tests (tests/unit)	25s
tests (src)	33s
coverage	59s
test	1s
	13m 13s

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