Feat/streaming savings report

[Achal13jain]

Summary

Adds streaming JSONL support for large record files and reports metadata reduction savings from fix.

This PR adds:

• scan --stream for JSONL inputs.
• validate --stream for JSONL inputs.
• fix --stream --format jsonl for one-record-at-a-time cleanup.
• Metadata reduction totals in fix output, including bytes removed and percentage reduction.
• Aggregate report counts for streaming scan/validate without storing every record in memory.
• Updated README, usage docs, changelog, and roadmap.

Testing

python -m pytest
ruff check .
ruff format --check .
mypy vectormeta

Results:

• 60 passed
• Ruff check passed
• Ruff format check passed
• Mypy passed

Checklist

• Core logic remains independent from Typer/Rich where practical.
• New behavior has focused tests.
• Docs or examples are updated when user-facing behavior changes.
• Vector database limit claims are cautious and sourced where needed.