v0.4.0 — data transfer rate, acceleration & illumination (20 categories)

v0.4.0 — three new categories: data transfer rate, acceleration, illumination (now 20 total)

New / 新增:

• data transfer rate — tbit/s…bit/s (decimal bits), tb/s…b/s (decimal bytes), tib/s…kib/s (binary bytes). The classic mix-up answered exactly: 100 Mbps = 12.5 MB/s. mb/s = megabyte/s (data-table rule), mbps/mbit/s = megabit/s.
• acceleration — m/s2, g0 (standard gravity 9.80665 m/s²), ft/s2, mph/s. 1 g = 32.174049 ft/s², 60 mph/s = 26.8224 m/s². g stays the gram — gravity is g0 / gravity / g-force.
• illumination — klx, lx (lux), fc (foot-candle, 1 fc = 10.76391 lx), ph (phot).
• The old data size / transfer category is now data size (sizes only); rates live in data transfer rate.

Still zero runtime dependencies, pure arithmetic, all outputs anchored to an independent Python oracle. 49 tests green, coverage 93.65%.

中文：v0.4.0 新增三个类别——数据传输速率（100 Mbps = 12.5 MB/s 精确换算；mb/s 为兆字节、mbps/mbit/s 为兆比特）、加速度（标准重力 g0、g-force、ft/s2、mph/s）、照度（lux/klx/英尺烛光 fc/辐透 ph）；原「数据大小/传输」类别更名为「数据大小」。共 20 个类别，零运行时依赖不变，锚点全部由独立 Python oracle 定值。