feat(chunkv5): Chunk V5 structure, encoding and decoding

[shantanualsi]

Add New Organized Chunk Format (V5)

Overview

This PR introduces a new chunk format (V5) for Loki that organizes log data into distinct sections: log lines, timestamps, and structured metadata. This organization enables more efficient querying by allowing selective decompression of only the required sections.

Changes

• Added new ChunkFormatV5 constant
• Implemented organisedHeadBlock for organizing data during writes
• Added organizedBufferedIterator for efficient reading of organized chunks
• Implemented serialization/deserialization for the new format
• Added comprehensive block organization and section management
• Modified query path to determine whether a metric query should need log lines to evaluate.

Current Status

This PR focuses on the storage format implementation and core functionality. The following aspects will be addressed in subsequent PRs:

Ongoing work:

1. Performance Benchmarking

   • Comprehensive benchmarks comparing V4 vs V5 formats
   • Memory usage analysis
   • Query performance metrics
   • Write performance impact

2. Migration Support

   • Tools for migrating existing chunks to V5 format
   • Backward compatibility handling

Design:

• Enables selective decompression of chunk sections
• Improves query performance for structured metadata and timestamp-based queries
• Better compression ratios due to grouping similar data types
• Cleaner separation of concerns in the codebase

Refer pkg/chunkenc/chunk-v5.md in this PR for more documentation

What this PR does / why we need it:

Which issue(s) this PR fixes:
https://github.com/grafana/loki-private/issues/1134

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR