fix: handle PromQL time binary aggregation

[fengjiachun]

What changed

• Skip non-Greptime table scans when collecting PromQL row-key tag metadata.
• Add regression coverage for sum/min/max/avg by (...) over time() - metric.

Why

Issue #8397 showed query_range returning 500 for aggregation over a binary expression involving time(). In v1.1.x, binary projections can retain __tsid for metric-engine optimization. The outer aggregate then inspects row-key metadata and may traverse the EmptyMetric dummy scan generated for time(), which is not backed by a Greptime table provider.

Validation

• cargo fmt --check
• cargo test -p query aggregate_over_binary_time_function_expr --lib -- --nocapture
• cargo test -p query tsid --lib

Fixes #8397

[gemini-code-assist]

Code Review

This pull request updates the PromQL planner in src/query/src/promql/planner.rs to handle derived PromQL plans that may contain non-Greptime scans without row-key metadata. It replaces the error propagation (?) with a conditional let Ok(table) check when retrieving a table from the source. Additionally, a new unit test aggregate_over_binary_time_function_expr has been added to verify aggregation behavior over binary time function expressions. I have no feedback to provide.

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