chore(flags): Add compression and serialization configuration to Redis clients

[haacked]

Problem

The Rust RedisClient needs to be compatible with Django's Redis caching behavior for seamless interoperability between Python and Rust services. Currently:

1. No compression support - Django uses Zstd compression for large values (>512 bytes) to reduce Redis memory usage and network overhead
2. Limited serialization options - Only Pickle format is supported, but different use cases need different formats (UTF-8 for simple strings, raw bytes for binary data)
3. Inconsistent configuration - No centralized way to configure compression and serialization behavior per client

Without these features, Rust services cannot properly read/write data that Django services cache, and vice versa.

Changes

Added configurable compression and serialization format support to RedisClient with Django-compatible defaults:

Compression Support (Zstd)

• CompressionConfig - Configures compression behavior with Django-compatible defaults:
  • enabled: true - Compression on by default
  • threshold: 512 - Matches Django's ZstdCompressor.min_length
  • level: 0 - Matches Django's default preset (equivalent to level 3)
• Graceful decompression - try_decompress() handles both compressed and uncompressed data, allowing gradual rollout
• Automatic compression - Values over threshold are automatically compressed on write

Serialization Format Support

• RedisValueFormat enum - Three formats for different use cases:
  • Pickle (default) - Django-compatible serialization
  • Utf8 - Simple string encoding
  • RawBytes - Direct binary data (via dedicated methods)
• Per-client configuration - Format is set once at client creation
• Per-call overrides - *_with_format() methods available when needed

API Design

Simplified constructor API:

// Default: compression disabled, Pickle format
let client = RedisClient::new(addr).await?;

// Full control over both settings
let client = RedisClient::with_config(
    addr,
    CompressionConfig::new(true, 512, 0),
    RedisValueFormat::Utf8,
).await?;

// Django-compatible: compression enabled, Pickle serialization
let client = RedisClient::with_config(
    addr,
    CompressionConfig::default(),  // 512-byte threshold, level 0
    RedisValueFormat::Pickle,
).await?;

How did you test this code?

cargo test --package common-redis --lib  # All 20 tests pass
cargo clippy --package common-redis --all-targets --all-features -- -D warnings  # No warnings

Tests cover:

• Compression behavior at various thresholds (below, at, above)
• Compression levels (0, custom levels)
• Round-trip serialization for all formats (Pickle, Utf8)
• Format interoperability (ensuring different formats produce different outputs)
• Decompression of both compressed and uncompressed data
• Error handling for invalid formats

Backwards Compatible

Existing code is not affected as defaults remain the same. Added a new ctor for configuring the client.

[Copilot]

Pull Request Overview

This PR adds zstd compression support to the Redis client library to match Django's compression behavior. The implementation allows for transparent compression/decompression of Redis values based on configurable thresholds.

• Adds CompressionConfig struct with Django-compatible defaults (512-byte threshold, level 0)
• Implements compression/decompression logic that gracefully handles both compressed and uncompressed data
• Updates RedisClient to store and use compression and format configurations

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

File	Description
rust/common/redis/src/lib.rs	Adds compression infrastructure, configuration types, helper methods, and comprehensive test coverage
rust/common/redis/Cargo.toml	Adds zstd dependency version 0.13
rust/Cargo.lock	Updates lock file with zstd dependency

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[greptile-apps]

_{2 files reviewed, 2 comments}

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[gustavohstrassburger]

Nice, I just noticed that the description of the PR mentions that CompressionConfig is enabled by default and you've changed that, so you might want to change there also.