Fix inner transport not closed

[yanyongyu]

The inner transport will be closed automatically when closing outer transport.
But, CacheConnectionPool wraps the pool of type RequestInterface, which do not have close method. I'm not sure how to fix the closing of pool.

fix #145

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cab9520) 100.00% compared to head (da33642) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #147   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           29        29           
  Lines         2063      2064    +1     
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+ Hits          2063      2064    +1     

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[karpetrosyan]

Looks great, thanks! For AsyncCacheConnectionPool and CacheConnectionPool, I'd recommend something like this:

    async def aclose(self) -> None:
        await self._storage.aclose()

        if hasattr(self._pool, "aclose"):  # pragma: no cover
            await self._pool.aclose()

This is what we use in httpcore for such cases.

[yanyongyu]

Updated. added close to cachepool