chore: Improve expression fallback reporting

[andygrove]

Which issue does this PR close?

Part of #2239

Part of #1974

Rationale for this change

We currently have two different approaches to expression fallback reporting.

• CometCast has different support levels Compatible, Incompatible, and Unsupported which are context sensitive (different types of cast have different support levels)
• Other expressions have IncompatExpr

This PR is a step towards unifying these approaches.

What changes are included in this PR?

• Remove IncompatExpr trait
• Add getSupportLevel method to CometExpressionSerde

How are these changes tested?

[codecov-commenter]

Codecov Report

❌ Patch coverage is 58.69565% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.51%. Comparing base (f09f8af) to head (7ef3abf).
⚠️ Report is 412 commits behind head on main.

Files with missing lines	Patch %	Lines
.../scala/org/apache/comet/serde/QueryPlanSerde.scala	20.83%	14 Missing and 5 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2240      +/-   ##
============================================
+ Coverage     56.12%   58.51%   +2.38%     
- Complexity      976     1281     +305     
============================================
  Files           119      143      +24     
  Lines         11743    13280    +1537     
  Branches       2251     2369     +118     
============================================
+ Hits           6591     7771    +1180     
- Misses         4012     4272     +260     
- Partials       1140     1237      +97     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[andygrove]

These move into QueryPlanSerde now that they are no longer specific to Cast

[mbutrovich]

LGTM, a couple of minor questions that don't require change:

• Should we prefer "Comet" over "we" in comments?
• Do we have an example of what kind of notes would be put in Compatible?

[andygrove]

* Should we prefer "Comet" over "we" in comments?

Yes, I can update this in the next PR (#2211)

* Do we have an example of what kind of notes would be put in `Compatible`?

We only have one example of this so far, when casting from String to Date:

Compatible(Some("Only supports years between 262143 BC and 262142 AD"))

So really, when we say "Compatible", we mean Compatible enough that we are willing to allow it by default.

[andygrove]

Thanks for the review @mbutrovich