fix(vikingdb): normalize created_at filters in API key client

[heaoxiang-ai]

Description

Fix date filtering for the commercial VikingDB data plane that uses Bearer API-key authentication. OpenViking keeps compiling TimeRange to its existing internal range DSL, while VolcengineApiKeyCollection now translates only created_at range nodes inside the outgoing filter to VikingDB time_range nodes.

This keeps the shared adapter behavior unchanged for local, cuVS, HTTP, Volcengine AK/SK, and custom backends.

Human Involvement

• A human participated in the implementation or review loop
• This PR was generated entirely by AI agents without human participation in the loop

Related Issue

N/A

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Normalize range to time_range only for created_at nodes in the outgoing VikingDB API-key client filter.
• Apply the conversion only to the request body filter; upsert and update data remain untouched.
• Preserve numeric range nodes and nested boolean filter structure.
• Add a client-boundary regression test covering the converted date filter and an unchanged numeric filter.

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Verified by directly invoking the focused client test with uv run python; the API-key client test passed, and an additional assertion confirmed the shared base adapter still emits range.

Also verified:

uvx ruff check openviking/storage/vectordb/collection/volcengine_api_key_collection.py tests/storage/test_volcengine_clients.py
uvx ruff format --check openviking/storage/vectordb/collection/volcengine_api_key_collection.py tests/storage/test_volcengine_clients.py
git diff --check

Checklist

• My code follows the project coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

N/A

Additional Notes

The local full pytest invocation exits with status 139 while loading the native-extension test environment. The focused client test itself passes when invoked directly.