fix(flame_3d): Use float for numLights uniform to fix GLES crash

[agnath18K]

Description

Fixes #3809

flame_3d crashes on Android GLES because spatial_material.frag declares uint numLights and lighting_info.dart sets it via shader.setUint(). Impeller's GLES backend only supports float uniforms — the uint path hits an unhandled shader type and crashes.

Changed uint → float in the shader and setUint → setFloat in Dart. The value is a light count (0–3) so float works identically. Recompiled the shaderbundle.

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 ///.
• I have updated/added relevant examples in examples or docs.

No test added — the crash only reproduces on a real GLES device/emulator, not in unit tests. The existing lighting logic is unchanged; only the uniform type is corrected.

Breaking Change?

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

[wolfenrain]

We should verify if this still works on iOS/macos

I don't mind changing it to an float, but if I recall we had weird float issues on the other platforms 😭