fix: filter empty preference memory items

[RerankerGuo]

Fixes #2006.

Summary

• Skip extracted preference entries whose normalized preference field is empty before creating PreferenceMemory items.
• Strip non-empty preference text before storing it in metadata.
• Add regression coverage for explicit and implicit preference extraction results that mix empty and valid entries.
• Convert touched preference-extractor log messages to parameterized logging while keeping behavior unchanged.

Validation

• python3 -m py_compile src/memos/mem_reader/read_pref_memory/process_preference_memory.py tests/mem_reader/test_preference_memory.py
• Manual line-length check for touched Python files passed.
• Attempted: python3 -m pytest tests/mem_reader/test_preference_memory.py -q; blocked because pytest is not installed in this environment.
• Attempted: make format; blocked because poetry is not installed in this environment.

[Memtensor-AI]

Automated Test Results: QUEUED

Conflict with dev-v2.0.22 was resolved by merging the base branch into this PR head. Local syntax check passed; cloud test-engine rerun has been queued.

• Run: tr-c36bee8d-bf7 on cloud test-engine 10010
• Branch tested: refs/pull/2011/head

I will post the final pass/fail result when the run completes.

[Memtensor-AI]

Automated Test Results: PASSED

Cloud test-engine rerun against dev-v2.0.22 completed successfully.

• Run: tr-c36bee8d-bf7 on cloud test-engine 10010
• memos_python_core/changed-repo-python: 2 passed, 0 failed, 0 skipped

Manual code review is still required before merge.

[RerankerGuo]

Hi @Memtensor-AI / @CarltonXiang — friendly ping on this draft.

Quick observation: this PR still has base branch main, but MemTensor/MemOS's current merge flow is into dev-v2.0.22 (every recent PR #2065 / #2058 / #2047 / #2046 / #2042 / #2034 / #2033 / #2026 lands on dev-v2.0.22). The bot already retargeted the base SHA for testing and cloud test-engine returned PASSED against dev-v2.0.22 on every rerun.

Could a maintainer please change the base branch from main → dev-v2.0.22 (Edit → base branch dropdown) so this can enter the normal merge queue? The head commit is a single focused change and does not depend on any main-only commits.

Thanks!

[RerankerGuo]

Hi @syzsunshine219 — looks like you've merged 35 of the last 50 PRs on this repo. Friendly ping on this one.

This draft (and the other 21 OPEN PRs I have here) is small, single-commit, has cloud test-engine PASSED, and is fully mergeable. The only thing blocking it is that the base branch dropdown still says main — every recent merge (e.g. #2038, #2037, #2034, #2032) landed on dev-v2.0.22.

When you have a moment, would you mind one of:

1. Flipping the base branch on this PR from main → dev-v2.0.22 (Edit → base branch dropdown), or
2. Telling me which base branch you'd prefer and I'll re-push accordingly.

Both fix and feature PRs in this batch are independent — each can be reviewed/merged on its own. Happy to rebase / split / drop any that don't fit the direction.

Thanks!