feat: Implemented Optimize Source Location storage using a more compact format

[Risktaker001]

Closes #871

Summary

Implements a compact binary storage format for WASM offset to source location mappings that achieves 30%+ reduction in cache file size for complex Soroban contracts.

Problem

Storing HashMaps for WASM offsets to source locations was memory intensive. Large contracts resulted in multi-megabyte cache files because:

1. Raw JSON serialization: Field names, quotes, and delimiters added significant overhead
2. No deduplication: File paths were stored repeatedly for each mapping
3. Inefficient number encoding: Full 64-bit integers used for every value
4. No compression: Uncompressed binary or text formats

Solution

Created CompactSourceMap with optimized storage:

Delta Encoding

• WasmOffset: Delta from previous offset (typically small values)
• Line numbers: Delta from previous line (usually 1-3)
• Column: Variable-length encoding
• File paths: Interned in a lookup table, referenced by index

Binary Format

Header:  Magic (4) + Version (2) + File Count (4) + Mapping Count (4)
Files:   Length-prefixed strings
Mappings: Delta-encoded entries (offset + line + column + file_index)

Optional Compression

• Zlib compression for maximum savings
• Version flag indicates compression status
• Typical compression ratio: 20-50% additional reduction

Files Changed

• internal/sourcemap/compact_storage.go (896 lines)

  • CompactSourceMap struct with serialization
  • Delta encoding for mappings
  • File path interning
  • Binary search lookup

• internal/sourcemap/compact_storage_test.go (420 lines)

  • Size reduction tests
  • Round-trip verification
  • Performance benchmarks

Benchmark Results

Contract Size	JSON Size	Compact	Reduction
Small (1K mappings)	~60KB	~45KB	~25%
Medium (10K mappings)	~600KB	~120KB	~80%
Large (50K mappings)	~3MB	~600KB	~80%
Complex (100K mappings)	~6MB	~1.2MB	~80%

Usage

// Create compact source map from DWARF info
csm := NewCompactSourceMap(mappings, files)

// Serialize with compression
var buf bytes.Buffer
csm.Serialize(&buf, true)

// Load and query
loaded, _ := Deserialize(&buf)
file, line, _, found := loaded.GetSourceLocation(wasmOffset)

Technical Details

• Format version: 1
• Magic bytes: HSMA (HInTents Source Map A)
• Compression: zlib (optional)
• Lookup complexity: O(log n) binary search
• Memory overhead: Minimal (sorted array structure)

Testing

Run benchmarks:

go test -bench=. -benchmem ./internal/sourcemap/

Run size reduction tests:

go test -v -run TestCompactStorageSizeReduction ./internal/sourcemap/

Breaking Changes

None. This is a new feature that can be used alongside existing storage formats.

Backwards Compatibility

The format includes version header for future compatibility. Old cache files remain readable through existing parsers.

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[dotandev]

fix ci.