refactor(storage): client uses transport stub

[dbolduc]

Part of the work for #2041

Implement the client::Storage using the transport::Storage stub. The next PR will genericize the stub.

On RequestOptions....

We need to hold onto the client options. In GAPICs, the transport stub will check if a given request option is supplied, and if not, it will use its own. All the types are Option<T>.

At the moment in storage, we have actual types that we default. So every request option passed along to the transport stub has a value. We would overwrite the client options (unless we store options in the client, and use those to initialize the builder).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.41%. Comparing base (6a2b52a) to head (cd36157).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3164   +/-   ##
=======================================
  Coverage   96.41%   96.41%           
=======================================
  Files         110      110           
  Lines        4431     4433    +2     
=======================================
+ Hits         4272     4274    +2     
  Misses        159      159           

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