feat: add back as_query method to AwaitableQuery

[seladb]

Description

Addresses #2056: bring back AwaitableQuery.as_query().

Motivation and Context

As described in #2056 there are cases where users have complex queries and need access to the internal pypika layer. The as_query() method used to exist but was removed in #1777. I don't see a reason why not to add it back.

How Has This Been Tested?

Yes, tests added int this PR.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

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_{Comparing seladb:add-back-as-query (cb0d601) with develop (c0de49f)}