Bug Fix: #60343 Construction of Series / Index fails from dict keys when "str" dtype is specified explicitly

[tasfia8]

• This PR fixes #60343 @jorisvandenbossche The default behaviour (pd.Index(d.keys())) worked correctly, but explicitly setting dtype="str" raised a ValueError. The issue stemmed from dict_keys not being converted to a proper array-like structure before being passed to StringDtype, which couldn't handle such inputs.

To fix the issue:

• KeyView was introduced to identify and preprocess dict_keys before passing them to Pandas internals. The keys are now converted to a list for compatibility.

• Updated logic in Index and sanitize_array to map dtype="str" to StringDtype(storage="python"). Updated check_array_indexer to allow empty boolean indexers for StringArray

• New test added "test_index_from_dict_keys_with_dtype" to ensure: Default inference (pd.Index(d.keys())) works. Explicit dtype="str" works, resulting in string[python].

• Updated existing tests (test_is_object and test_empty_fancy) to handle new behaviours introduced by the fix.

After the fix both the default (pd.Index(d.keys())) and explicit (pd.Index(d.keys(), dtype="str")) cases work:

[tasfia8]

Hi, I'm a student contributing to this PR and am on bit of a time crunch due to finals. For my school project, my task is to merge the PR as quickly as possible with the help and guidance of maintainers. I was able to fix the bug but I am a bit stuck on how to fix the checks. Could @jorisvandenbossche or anyone else help? Especially the unit tests ones. I tried to fix the pre-commit (using ruff lint fix) but every time I fixed a formatting issue, after running pre-commit it goes to the initial position before I did the fix.

For the Doc build and upload check (it was giving an error for every declaration of ipython that didn't have import pandas as pd), I manually inserted it but don't know if there is an easy way.