feat: async api

[sighphyre]

Adds a small async api variant to support the incoming async client

[coveralls]

Pull Request Test Coverage Report for Build 19260300150

Details

• 91 of 102 (89.22%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.5%) to 92.805%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
UnleashClient/api/async_api.py	83	94	88.3%

Totals
Change from base Build 19061071890:	-0.5%
Covered Lines:	761
Relevant Lines:	820

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💛 - Coveralls