fix: Ray direction normalization drift issues

[ufrshubham]

Description

raytrace() reuses the same RaycastResult objects across bounces, so the reflected direction from one bounce becomes the incident direction for the next. Vector2.reflect() is not bit-exact, so each bounce introduces a tiny floating-point rounding error. After enough bounces the direction's length drifts just past the 1e-6 tolerance that Ray2 enforces, causing a direction must be normalized assertion crash.

Two fixes:

• CircleHitbox and PolygonRayIntersection (used by RectangleHitbox / PolygonHitbox): call normalize() on the reflected direction before passing it to Ray2, so drift is corrected on every bounce.
• raytrace_example: the initial ray direction was set via a cascade on the Vector2 getter (ray.direction..setValues(...)), which bypasses the direction= setter and leaves the cached inverse values stale. Fixed to assign through the setter.

Regression tests are included that inject a direction whose length² is already above the threshold (by writing directly to the underlying Vector2, bypassing the setter), then assert that raycast() does not throw.

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• [NA] I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

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