Add optional component query filter

[waynemwashuma]

Objective

Introduces an optional ECS query filter that allows queries to return entities even when a selected component is absent.

Solution

Queries now distinguish between required and optional component descriptors. Optional components do not affect archetype matching and resolve to undefined when absent.

Changes Made

• Added the Optional query filter and optional() helper.
• Added QueryFilter.isRequired() for determining which components must exist in an archetype.
• Updated queries to match archetypes using only required descriptors.
• Added type-level filter transforms so optional components are typed as Component | undefined.
• Applied transformed tuple types to get(), single(), each(), and eachCombination().
• Exported the new filter types.

Why This Approach

This keeps the component selection order unchanged while allowing systems to access related components without creating separate queries for every component combination. The type transformation also ensures consumers handle potentially absent components safely.

Showcase

Before

const query = new Query(world, [Position, Velocity])

Only entities containing both Position and Velocity matched the query.

After

const query = new Query(world, [Position, Velocity], [optional(Velocity)])

query.each(([position, velocity]) => {
  // velocity is `Velocity | undefined`
})

Entities containing Position now match regardless of whether they contain Velocity or not.

Migration Guide

No migration required.

Checklist

• I have updated the documentation accordingly.
• I have added tests to cover my changes.