Python: improve the filtering of in-memory vector stores

[eavanvalkenburg]

Motivation and Context

Slight improvement to the in-memory vector store filtering.

Description

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[moonbox3]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
connectors
in_memory.py	169	23	86%	69–70, 74, 78–81, 116, 128, 130, 171, 175, 179, 194, 211, 226, 275–276, 278, 285–286, 291, 326
TOTAL	28063	4812	82%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3787	23 💤	0 ❌	0 🔥	1m 45s ⏱️