Fix handling of PurePosixPath in PDFReader

[Anitha6g]

Description

Solution to bug - #16602 - S3Reader: Failed to load files other than .txt using S3Reader

ISSUE:
Failed to load file test-llamaindex/file1.docx with error: Attempt to open non key-like path: test-llamaindex\file1.docx. Skipping...
Failed to load file test-llamaindex/file2.pdf with error: RetryError[<Future at 0x1122b0b42b0 state=finished raised ValueError>]. Skipping...

Version
llama_index Version: 0.11.18, llama-index-readers-s3 Version: 0.2.0

Steps to Reproduce
This is the code used

`from llama_index.readers.s3 import S3Reader
from llama_index.readers.file import PDFReader, DocxReader

reader = S3Reader(
bucket="test-llamaindex",
aws_access_id=AWS_ACCESS_KEY_ID,
aws_access_secret=AWS_SECRET_ACCESS_KEY,
aws_session_token=AWS_SESSION_TOKEN,
recursive=True,
required_exts=[".pdf", ".docx", ".txt"],
file_extractor={".pdf": PDFReader(), ".docx": DocxReader()}
)
documents = reader.load_data()
documents`

DEBUGGED:
The issue is in the class PDFReader, in the below condition-
"""Parse file."""
if not isinstance(file, Path):
file = Path(file)
Since my file was of type <class 'pathlib.PurePosixPath'>, the IF condition passed and the Path(file) changes the "/" in the file path to "" which is not supported by s3fs and gives this error -
Attempt to open non key-like path: test-llamaindex\ShortStartStopMove.pdf
in line with fs.open(str(file), "rb") as fp:

SOLUTION:
Converting the file into posix path.
"""Parse file."""
if not isinstance(file, Path) and not isinstance(file, PurePosixPath):
file = PurePosixPath(file)

Fixes # (issue)
#16602

New Package?

PurePosixPath

Did I fill in the tool.llamahub section in the pyproject.toml and provide a detailed README.md for my new integration or package?

• Yes
• [ Y] No

Version Bump?

No

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• [ Y] No

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Your pull-request will likely not be merged unless it is covered by some form of impactful unit testing.

• I added new unit tests to cover this change
• [Y ] I believe this change is already covered by existing unit tests

Suggested Checklist:

• [Y] I have performed a self-review of my own code
• [Y] I have commented my code, particularly in hard-to-understand areas
• [ Y] I have made corresponding changes to the documentation
• I have added Google Colab support for the newly added notebooks.
• [ Y] My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• [ Y] New and existing unit tests pass locally with my changes
• [ Y] I ran make format; make lint to appease the lint gods