feat: configurable compression parameters API

[polaz]

Summary

The C reference exposes fine-grained compression parameters (windowLog, hashLog, chainLog, searchLog, minMatch, targetLength, strategy) that users can tune independently. This is essential for domain-specific optimization.

C reference API

ZSTD_CCtx_setParameter(cctx, ZSTD_c_windowLog, 22)
ZSTD_CCtx_setParameter(cctx, ZSTD_c_hashLog, 18)
ZSTD_CCtx_setParameter(cctx, ZSTD_c_strategy, ZSTD_lazy2)
// ... etc
ZSTD_cParam_getBounds(param)  // Query valid ranges

Current Rust state

• Only CompressionLevel enum with fixed parameter sets
• No way to override individual parameters
• Matcher trait allows custom algorithms but no parameter tuning of built-in ones

What needs to be implemented

1. CompressionParameters struct — all tunable parameters
2. Builder API — CompressionParameters::builder().window_log(22).hash_log(18).build()
3. Bounds checking — validate parameter ranges
4. Level-to-params mapping — each level maps to a default parameter set
5. Integration with FrameCompressor — accept parameters instead of just level

Acceptance criteria

• All C zstd compression parameters exposed
• Builder pattern with validation
• Custom parameters produce valid output
• Level-based defaults match C zstd parameter tables

Dependencies

• feat: implement Default compression level (zstd level 3, dfast strategy) #5-feat: implement Best compression level (zstd level 11, btlazy2 strategy) #7 (compression level implementations) for strategies
• feat: numeric compression levels (1-22) API #21 (numeric levels) for level mapping

Time estimate

1d

Blocked by

• feat: numeric compression levels (1-22) API #21 (Numeric levels) — parameter API depends on level-to-params mapping
• feat: implement Default compression level (zstd level 3, dfast strategy) #5, feat: implement Better compression level (zstd level 7, lazy2 strategy) #6, feat: implement Best compression level (zstd level 11, btlazy2 strategy) #7 — strategy implementations must exist to be configurable

[coderabbitai]

🔗 Related PRs

#2 - feat: managed fork setup — README, FUNDING, crate rename to structured-zstd [merged]

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