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GH-37306: [Go] Add binary dictionary unifier (#37309)

The "generic" dictionary unifier is fine for starting out, but causes unnecessary CPU cycles because of the `getvalFn` returning `interface{}` and the ramifications of it.

Fixes #37306

### Rationale for this change

See #37306

### What changes are included in this PR?

An optimized version of a unifier for binary dictionaries.

### Are these changes tested?

Tested by using it within [Parca](https://github.com/parca-dev/parca).

### Are there any user-facing changes?

This is a new API.
* Closes: #37306

Authored-by: Frederic Branczyk <fbranczyk@gmail.com>
Signed-off-by: Matt Topol <zotthewizard@gmail.com>