feat(stdlib): add colorsys module — color space conversions

[antonsynd]

Summary

Add a colorsys module for converting between color systems (RGB, HSV, HLS, YIQ), matching Python's colorsys module API. Pure math, no dependencies.

Proposed Sharpy API

import colorsys

h, s, v = colorsys.rgb_to_hsv(0.2, 0.4, 0.6)
r, g, b = colorsys.hsv_to_rgb(h, s, v)

h, l, s = colorsys.rgb_to_hls(0.2, 0.4, 0.6)
r, g, b = colorsys.hls_to_rgb(h, l, s)

y, i, q = colorsys.rgb_to_yiq(0.2, 0.4, 0.6)
r, g, b = colorsys.yiq_to_rgb(y, i, q)

Key Decisions

• All values are floats in [0.0, 1.0] range (matching Python)
• Hue is in [0.0, 1.0] (not degrees — matching Python)
• Pure functions, no classes needed
• Smallest possible module — 6 functions, ~100 lines
• Match Python's exact formulas for bit-perfect compatibility

Test Plan

• RGB to HSV roundtrip
• RGB to HLS roundtrip
• RGB to YIQ roundtrip
• Edge cases (black, white, pure colors)
• Boundary values (0.0, 1.0)
• Match Python output for known inputs

[antonsynd]

Implemented in ce6a757 (feat(stdlib): add colorsys, pprint, calendar, and zoneinfo modules). Module includes all 6 conversion functions (RGB↔HSV, RGB↔HLS, RGB↔YIQ) with comprehensive test coverage in ColorsysTests.cs.