Copybara import of the project:
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004b932434596efb9d0e52a4f84179e9f8a7263d by jorisSchaller <71265553+jorisSchaller@users.noreply.github.com>:
Refactor pooling operation
- Pooling operation moved out of Linen
- Pooling documentation duplicated in nnx
PiperOrigin-RevId: 842406713
