Reduce implementation complexity

[erindru]

I started reviewing TobikoData#4751 again but quickly realised there were some more fundamental problems. Namely, a lot of things were implemented that did not need to exist and I figured that there would be a lot of back-and-forth that would ultimately just end up getting fed into Claude and not actually addressing the underlying problems.

So this PR does the following:

• Strip out a bunch of the vibe code in favour of re-using existing constructs
• Change CatalogSupport.FULL_SUPPORT to CatalogSupport.REQUIRES_SET_CATALOG because it seems far more operations than not need the catalog to be set, including querying INFORMATION_SCHEMA
• Refactor the HTTP code into a separate class to keep it contained and remove some of the boilerplate
• Remove unnecessary checks like "ensure schema exists before creating view or table" - SQLMesh already does this
• Simplify connection factory override in FabricEngineAdapter constructor
• Fix unit tests

The result passes our integration test suite but I didn't run it against an actual project.

@fresioAS if you have something locally do you mind doublechecking it?

[fresioAS]

Thank you @erindru !

I will run this on my live project tomorrow and report back!