Track individual expr's execution time in `ProjectExec` metrics (in `EXPLAIN ANALYZE`)

### Is your feature request related to a problem or challenge?

Originally suggested by @simonvandel in https://github.com/apache/datafusion/issues/18217#issuecomment-3472801129

> ProjectionExec currently shows the total elapsed time for all expressions. Would it make sense to show timings for each individual expression? Perhaps we could do it in VERBOSE mode

Given query (executed in `datafusion-cli`:
```
> set datafusion.explain.analyze_level = summary;
0 row(s) fetched.
Elapsed 0.001 seconds.

> explain analyze select pow(v1,2), abs(round(sqrt(v1)))
from generate_series(1000) as t1(v1);
+-------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| plan_type | plan |
+-------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Plan with Metrics | ProjectionExec: expr=[power(v1@0, 2) as pow(t1.v1,Int64(2)), abs(round(sqrt(CAST(v1@0 AS Float64)))) as abs(round(sqrt(t1.v1)))], metrics=[output_rows=1001, elapsed_compute=167.513µs, output_bytes=15.8 KB] |
| | RepartitionExec: partitioning=RoundRobinBatch(14), input_partitions=1, metrics=[spill_count=0, spilled_bytes=0.0 B, spilled_rows=0, fetch_time=48.126µs, repartition_time=1ns, send_time=6.055µs] |
| | ProjectionExec: expr=[value@0 as v1], metrics=[output_rows=1001, elapsed_compute=2.458µs, output_bytes=64.0 KB] |
| | LazyMemoryExec: partitions=1, batch_generators=[generate_series: start=0, end=1000, batch_size=8192], metrics=[output_rows=1001, elapsed_compute=35.208µs, output_bytes=64.0 KB] |
| | |
+-------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row(s) fetched.
Elapsed 0.006 seconds.
```
In `ProjectExec`'s metric, we can track each expressions evaluation time separately like `pow(v1,2): 10ms, abs(round(sqrt(v1))): 30ms`, this should be easy to implement.

Additionally, we can also implement fine-grained execution time tracking for nested expression like `sqrt(v1): 5ms, round(sqrt(v1)): 10ms, abs(round(sqrt(v1))): 15ms`.
I have briefly checked the implementation, it requires a) public API change that enables metrics tracking for `Expr`s b) Update implementation for expressions.
I think we don't have to implement that for all builtin `Expr`s, the math expressions as showed in the example are usually very fast, however there are some expressions that are slower to evaluate, and regularly cause performance issue (e.g. `array_` functions, regex functions), it can be helpful to track execution time for them.

### Describe the solution you'd like

- [ ] Implement per-expression metrics tracking in `ProjectionExec`
- [ ] Support fine-grained execution time metric for individual `Expr`s in a nested expression.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_