BUG: Fix GroupBy aggregate coersion of outputs inconsistency for pyarrow dtypes
- [x] closes #61636
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [x] Added an entry in the latest `doc/source/whatsnew/v3.0.0.rst` file if fixing a bug or adding a new feature.

## Description
Fix a bug in `DataFrameGroupBy.agg` when applied to columns with `ArrowDtype`, where pandas attempted to cast the result back to the original dtype.

## Cause
1. `ExtensionArray._from_scalars()` should raise only `ValueError` or `TypeError`, instead of `pa.ArrowNotImplementedError`.
2. `ArrowExtensionArray._from_sequence()` may attempt an invalid cast, and if it succeeds, it can unintentionally alter the actual data type.
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