feat: Track individual expr's execution time in ProjectionExec metrics

[va24nsh]

Which issue does this PR close?

• First Part of Track individual expr's execution time in ProjectExec metrics (in EXPLAIN ANALYZE) #18456

Rationale for this change

Currently, EXPLAIN ANALYZE for ProjectionExec only shows aggregated metrics like total elapsed compute time, but doesn't provide visibility into how much time individual expressions within the projection consume. This makes it difficult to identify performance bottlenecks when debugging slow queries with complex projection expressions.

What changes are included in this PR?

1. Enhanced ProjectionExec with per-expression timing metrics:
- Added per-expression Time metrics collection in ProjectionStream
- Each projection expression gets its own timer using the expression alias as the metric name
- Metrics are properly registered with the execution plan's metrics set

2. Extended metrics display in EXPLAIN ANALYZE:
- Modified display.rs to detect ProjectionExec plans
- Added get_projection_expr_metrics() helper function to extract per-expression timing data
- Enhanced metrics output to include per-expression times alongside standard metrics

3. Added intelligent time formatting:
- Implemented proper time unit formatting (ns, μs, ms, s) based on duration magnitude
- Maintains consistency with DataFusion's existing time formatting standards

Are these changes tested?

Yes - The tests have been added to check the proper functionality of latest functions.

Are there any user-facing changes?

Yes - This is an enhancement to the existing EXPLAIN ANALYZE functionality

[2010YOUY01]

Thanks for the efforts, but I'll skip follow-up due to https://datafusion.apache.org/contributor-guide/index.html#why-fully-ai-generated-prs-without-understanding-are-not-helpful