refactor: reduce internal EagerSnapshot usage

[ethan-tyler]

This removes internal EagerSnapshot dependencies where the code can use Snapshot, Arc<Snapshot>, active add APIs, tombstone APIs, DeltaScanNext, or FileSelection directly. Public compatibility stays intact.

[codecov]

Codecov Report

❌ Patch coverage is 86.71096% with 40 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.03%. Comparing base (e87d969) to head (210d308).

Files with missing lines	Patch %	Lines
...re/src/delta_datafusion/table_provider/next/mod.rs	78.37%	0 Missing and 16 partials ⚠️
crates/core/src/delta_datafusion/find_files.rs	72.34%	0 Missing and 13 partials ⚠️
crates/core/src/operations/vacuum.rs	89.04%	0 Missing and 8 partials ⚠️
crates/core/src/operations/filesystem_check.rs	50.00%	0 Missing and 1 partial ⚠️
crates/core/src/operations/merge/mod.rs	75.00%	0 Missing and 1 partial ⚠️
crates/core/src/table/state.rs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4567      +/-   ##
==========================================
+ Coverage   80.00%   80.03%   +0.02%     
==========================================
  Files         179      179              
  Lines       64140    64286     +146     
  Branches    64140    64286     +146     
==========================================
+ Hits        51315    51449     +134     
+ Misses       9834     9825       -9     
- Partials     2991     3012      +21     

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[hntd187]

Now with even more .snapshot() !!

[hntd187]

I'll be honest, I think this may shift the usage instead of actually reducing it. There are a lot of places where there was no .snapshot() and now there is a call and a lot of places where there are now more .snapshot() on top of the prior call sites.

I think this needs a bit more re-thinking in general and I think we should just rip the band-aid off. Why did we create different kinds of snapshots in the first place? Because the implementation details are different right? If that is the case is this not something we can collate into a trait and just pass a single "Snapshot" around instead of having to do this snapshot().snapshot().snapshot() things, which seems really ugly. If the different kinds of snapshots are so different they cannot be represented in a single trait then let's discuss more.

[ethan-tyler]

going to keep this as a draft for now with it likely being superseded. A new issue was created to track a more robust snapshot design and future state here #4584.