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GH-34440: [Ruby] Add support for `RecordBatch{File,Stream}Reader#each` without block (#34441)

### Rationale for this change

`#each` must support this.

### What changes are included in this PR?

`to_enum` and tests for this.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

Yes.
* Closes: #34440

Lead-authored-by: Sutou Kouhei <kou@clear-code.com>
Co-authored-by: Sutou Kouhei <kou@cozmixng.org>
Co-authored-by: Hirokazu SUZUKI <heronshoes877@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>