pw_status: Introduce StatusBase and rework Status

StatusBase is a zero-cost CRTP status base class used to define
Status-like objects with custom status codes. A designated code value
represents success (ok()).

This enables richer, domain-specific status semantics while preserving
standard Pigweed error handling conventions, including PW_TRY,
PW_CHECK_OK, and PW_ASSERT_OK.

Custom status types can be defined using the PW_STATUS_TYPE macro or by
subclassing StatusBase directly with CRTP. Custom status types are
constructed from their Code.

pw::Status is reworked to be a concrete final class that inherits from
StatusBase<Status, PW_STATUS_OK>, retaining all canonical helper methods
and implicit pw_Status interop. PW_TRY and PW_CHECK_OK continue to
accept types implicitly convertible to pw::Status.

Change-Id: I33acb7f507f7e7290f0eae45edbc53eff007abb1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/477645