v0.7.0 — Frame-of-Reference + Bit Packing

What's New

Frame-of-Reference (FOR) Encoding

• 4–8× memory reduction for bounded numeric columns (ages, scores, ratings)
• Stores min once, bit-packs deltas into Python int bitmask
• Auto-detects after sampling threshold (default 50 rows)
• Auto-fallback when range exceeds 16 bits
• Per-column via for_columns=[] on ColumnarTable
• Transparent API — reads return full values, no changes needed
• Update fallback to raw (same pattern as delta encoding)

Impact

Scenario	Raw	FOR	Reduction
Ages 18-65 (100K rows)	400 KB	~88 KB	4.5×
Scores 0-100 (100K rows)	400 KB	~88 KB	4.5×

Tests

• 6 new tests added, all passing
• Zero regressions: 47 existing + 20 dict + 79 delta = 146 tests all pass

Closes

• #3