Optimize character_length UDF performance

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

Make it faster

### Describe the solution you'd like

We can make it faster by reusing the inlined view length and apply some other micro-optimizations

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by locating the character_length UDF implementation and the inlined view-length handling in DataFusion. Measure its current performance, then verify that reusing the inlined length and applying the proposed micro-optimizations makes the function faster without changing its results.

Written by the indexing model from the issue text.