[blog post] Spark compatibility testing

### What is the problem the feature request solves?

There have been some discussions around writing technical deep dive blog posts on the DataFusion blog. I would like to see if there is interest in a blog post focussing on Spark compatibility testing.

Possible topics:

- Challenges (different floating point implementation, regexp, unicode differences, date/time range differences)
- QueryPlanSerde overview - framework for context-specific tagging as Compatible, Incompatible, Unsupported
- Lessons learned from Fuzz testing approach
- Standalone fuzz testing vs fuzz testing in unit/integration tests
- Lessons learned from agentic coding
- Testing against multiple Spark versions
- Shims
- SQL-based testing, inspired by sqllogictest

### Describe the potential solution

_No response_

### Additional context

_No response_