chore: Improve reporting of fallback reasons for CollectLimit

[andygrove]

Which issue does this PR close?

Part of https://github.com/apache/datafusion-comet/issues/1669

Rationale for this change

I found it confusing to see CollectLimitExec is not supported, because I know that it is supported (in some cases).

What changes are included in this PR?

Improve reporting of fallback reasons.

How are these changes tested?

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.

Project coverage is 58.85%. Comparing base (f09f8af) to head (44dda6d). Report is 276 commits behind head on main.

Files with missing lines	Patch %	Lines
...n/scala/org/apache/comet/rules/CometExecRule.scala	94.44%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1694      +/-   ##
============================================
+ Coverage     56.12%   58.85%   +2.72%     
- Complexity      976     1141     +165     
============================================
  Files           119      130      +11     
  Lines         11743    12844    +1101     
  Branches       2251     2417     +166     
============================================
+ Hits           6591     7559     +968     
- Misses         4012     4065      +53     
- Partials       1140     1220      +80     

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[andygrove]

Thanks for the reviews @parthchandra and @kazuyukitanimura