[EuiSelectable] Add compressed prop

**Problem Statement**

some of our components, eg EuiComboBox, EuiSuperSelect have prop compressed
To be consistent in our pages, I expect that EuiSelectable also has it, but it dont

**Proposed Solution**

do the same as other components

**Use Case**

Opex autoops

**Value / Impact**

to be consistent

**Urgency**

~It is urgent, some our components already compressed~

It is **not** high priority. It's a nice-to-have for consistency. The other components have been reverted to non-compressed for consistency across pages.

**Do alternatives or workarounds exist?**

- Reverting to non-compressed when `EuiSelectable` is used with other components that do support smaller size.

**Additional context (Optional)**

(https://elastic.slack.com/archives/C7QC1JV6F/p1762241288529209)

**Designs or Specs (Optional)**

Non-final designs: https://www.figma.com/design/wNzNpBXzNTuoOWGacTAxxd/AutoOps--Angular-%E2%86%92-React?node-id=1086-55866&t=k8SNcJO5Wvef1JYO-0