[Ruby] Add `ArrowFormat::FixedSizeListArray.new(type, values)`

### Describe the enhancement requested

GH-50382 tracks a public builder API for `red-arrow-format`. In [the maintainer discussion](https://github.com/apache/arrow/issues/50382#issuecomment-5597093908), the requested direction is to support explicit constructors for all existing `ArrowFormat::Type` subclasses before exposing the broader builder API, with nested types handled as separate tasks.

`ArrowFormat::FixedSizeListArray` currently only accepts the low-level reader/writer form:

```ruby
ArrowFormat::FixedSizeListArray.new(type, size, validity_buffer, child)
```

Add the object-oriented values form:

```ruby
ArrowFormat::FixedSizeListArray.new(type, values)
```

The constructor should preserve the existing low-level form, validate that every non-null list has exactly the declared fixed size, build the parent validity bitmap, preserve the required fixed number of child slots for null parents, and delegate child construction to the declared child field type.

This is a focused prerequisite for GH-50382 and is separate from variable-size `ListArray` support in GH-51262.

### Component(s)

Ruby