feat: Add P95 latency metrics alongside P99 system-wide

[akhilpathivada]

📋 Summary

Adds P95 (95th percentile) latency metrics alongside existing P99 metrics across all VectorDBBench components for more comprehensive performance analysis.

🎯 Motivation

• P95 provides a middle ground between P99 (slowest 1%) and average latency
• More actionable for optimization compared to P99 alone
• Industry standard metric for performance monitoring

🔧 Key Changes

• Backend: Added P95 calculation in serial, concurrent, and streaming runners
• Frontend: Added P95 selection option in streaming and concurrent pages
• Results: Added P95 column to results table and exports
• Backward Compatibility: Existing result files show 0.0 for P95 metrics

🎮 Usage

# Streaming/Concurrent pages now offer P95 option
latency_type = st.radio("Latency Type", options=["latency_p99", "latency_p95", "latency_avg"])

Results Table:

latency(p99)	latency(p95)	recall
12.5ms	8.3ms	0.95

🧪 Testing

• All files compile successfully
• Backward compatibility with existing result files
• No breaking changes to existing APIs

📊 Impact

Generic support across all database clients and test cases. Users can now choose between P99 and P95 latency metrics based on their analysis needs.

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: akhilpathivada
To complete the pull request process, please assign xuanyang-cn after the PR has been reviewed.
You can assign the PR to them by writing /assign @xuanyang-cn in a comment when ready.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[akhilpathivada]

/assign @XuanYang-cn @alwayslove2013

[alwayslove2013]

@akhilpathivada plz fix the lint issues~

pip install black ruff --upgrade
make format
make lint

[akhilpathivada]

Please review the new PR instead due to commit history issues: #573

Same functionality, cleaner Git history. Thank you!