Fix reusable reference filter builders

[mameikagou]

Fixes #2143.

Reference filter targets were mutated when a terminal filter operation built its path. Reusing either the root reference builder or a derived property builder could therefore fail or reuse altered state.

Build each target path from a deep copy so independent filters do not share mutations.

Validation:

• test/collection/test_filter.py: 33 passed
• Ruff check and format passed
• compileall and diff checks passed

[orca-security-eu]

Orca Security Scan Summary

Status	Check	Issues by priority
Passed	Infrastructure as Code	0   0   0   0	View in Orca
Passed	SAST	0   0   0   0	View in Orca
Passed	Secrets	0   0   0   0	View in Orca
Passed	Vulnerabilities	0   0   0   0	View in Orca

[weaviate-git-bot]

To avoid any confusion in the future about your contribution to Weaviate, we work with a Contributor License Agreement. If you agree, you can simply add a comment to this PR that you agree with the CLA so that we can merge.

beep boop - the Weaviate bot 👋🤖

PS:
Are you already a member of the Weaviate Forum?

[mameikagou]

To avoid any confusion in the future about your contribution to Weaviate, we work with a Contributor License Agreement. If you agree, you can simply add a comment to this PR that you agree with the CLA so that we can merge.

beep boop - the Weaviate bot 👋🤖

PS:
Are you already a member of the Weaviate Forum?

I agree