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GH-39488: [Ruby] Add support for ChunkedArray in Ractor (#39490)

### Rationale for this change

We can't use `@ cache ||= build_cache` idiom in Ractor because Ractor requires that shared objects are immutable.

### What changes are included in this PR?

Compute caches before making ChunkedArray immutable.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

Yes.
* Closes: #39488

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>