fix(color): round channel bytes in default color hex serialization

[Pcmhacker-piro]

Resolves #9124

Changes:

In p5.js 2.x, toHexComponent in src/color/p5.Color.js used bitwise NOT truncation (const vInt = ~~(v * 255);) to convert normalized channel values to hex bytes.

Because truncation drops the fractional part toward zero:

• Any color channel producing a fractional byte (such as colorMode(RGB, 100); color(50, 0, 0), where 0.5 * 255 = 127.5) was truncated to 127 (#7f0000) instead of 128 (#800000).
• The cached default string returned by c.toString() (which p5.Renderer2D feeds into canvas ctx.fillStyle and ctx.strokeStyle) disagreed with c.toString('#rrggbb') on the exact same color object, because the #rrggbb formatting path goes through colorjs.io serialization and rounds to the nearest integer.
• Canvas rendering for colors with fractional channel bytes rendered one code point darker than expected.

This PR:

• Updates toHexComponent in src/color/p5.Color.js to use Math.round(v * 255).
• Adds unit tests in test/unit/color/p5.Color.js verifying that default c.toString() rounds fractional channel values correctly across custom color mode ranges (RGB, 100), standard 255 range (127.5), and alpha channels (127.5), ensuring strict consistency with c.toString('#rrggbb').

---

Verification:

1. Animated Demo Video (Terminal & Test Run)

2. Terminal Output & Verification

---

PR Checklist

• npm run lint passes
• Inline reference is included / updated (N/A, internal bug fix)
• Unit tests are included / updated

[Pcmhacker-piro]

Hi @limzykenneth (Color area steward) and @ksen0! 👋

Could you please take a look at this PR when you get a chance?

It addresses issue #9124 by updating toHexComponent from bitwise NOT truncation (~~) to standard rounding (Math.round), ensuring c.toString() strictly matches c.toString('#rrggbb') for fractional channel values.

• All 100 color unit tests are passing (including 3 new tests added for fractional RGB and alpha byte rounding).
• npm run lint exits clean with 0 errors.
• Terminal proof screenshot and animated workflow demonstration are included in the description.

Thank you so much!