Add `ParserOptions` support to `readExcel` for consistent parsing configuration

### Problem

`readExcel` currently does not support configurable parsing options, unlike other readers (e.g. CSV).

This creates inconsistency in the IO API:
- users can configure parsing behavior for some formats
- but cannot do the same for Excel
- behavior is fixed and may not fit all use cases

The need for configurable parsing was previously raised in discussion.

### Expected

Allow users to configure parsing behavior when reading Excel files.

### Acceptance criteria

- `readExcel` provides an overload accepting parsing configuration (e.g. `ParserOptions` or equivalent)
- Behavior is consistent with other readers (such as CSV)
- Default behavior remains unchanged for simple use cases
- Parsing configuration is documented and discoverable

### Motivation

- IO APIs should be consistent across formats
- Users expect similar configuration capabilities for all readers
- Lack of configuration reduces flexibility when working with Excel data
- Should be aligned before 1.0 API stabilization

As were suggested here:
https://github.com/Kotlin/dataframe/issues/1166#issuecomment-2842080733