fix(input): ignore blank lines when reading JSONL files

[VectorPeak]

Description

Fix JSONL input loading so blank or whitespace-only lines do not cause the entire .jsonl file to be skipped.

JSONLinesFileReader.read_file() currently parses every entry returned by text.splitlines() with json.loads(line). When a .jsonl file contains a blank line between otherwise valid records, json.loads("") raises JSONDecodeError. That exception bubbles up to InputReader._iterate_files(), which logs the error and skips the whole file.

This change filters out blank or whitespace-only lines before parsing JSONL records, while preserving the existing behavior for non-empty malformed JSON lines.

Related Issues

Fixes #2424.

Proposed Changes

• Ignore blank or whitespace-only lines when reading JSONL input files.
• Preserve existing parsing behavior for valid non-empty JSONL records.
• Preserve failure behavior for genuinely malformed non-empty JSONL lines.
• Add a focused unit test covering valid JSONL records separated by blank lines.

Checklist

• I have tested these changes locally.
• I have reviewed the code changes.
• I have updated the documentation (if necessary).
• I have added appropriate unit tests (if applicable).

Additional Notes

What Problem This Solves

A JSONL input file may contain accidental blank or whitespace-only lines between otherwise valid records:

{"text":"a"}

{"text":"b"}

Before this change, the blank line was passed directly to json.loads(""), which raises JSONDecodeError. Because InputReader._iterate_files() catches exceptions at the file level, the reader skipped the entire file instead of loading the valid records before and after the blank line.

Evidence

The affected call chain is:

create_input_reader(...)
  -> JSONLinesFileReader.read_file(...)
    -> text.splitlines()
    -> json.loads(line)
       -> JSONDecodeError on blank line
  -> InputReader._iterate_files(...)
    -> catches exception
    -> logs warning
    -> skips the file

This PR only ignores blank or whitespace-only JSONL lines. Malformed non-empty lines still go through json.loads(line) and keep the existing error/skip behavior.

Scope

This change only affects JSONL input handling. It does not change CSV, JSON, text, parquet, MarkItDown, storage behavior, or handling of malformed non-empty JSONL records.

Validation

• git diff --check
• uv run ruff format --check packages/graphrag-input/graphrag_input/jsonl.py tests/unit/indexing/input/test_jsonl_loader.py
• uv run ruff check packages/graphrag-input/graphrag_input/jsonl.py tests/unit/indexing/input/test_jsonl_loader.py
• uv run --package graphrag-input pytest tests/unit/indexing/input/test_jsonl_loader.py -q - 3 passed