feat: SnmpHealthProfile, the OIDs a driver declares; deprecate HealthMetricsMixin (4.12.0)

Drivers no longer collect over SNMP (docs/STRUCTURE.md). A driver whose
device publishes its health values under OIDs of its own declares them
as SNMP_HEALTH_PROFILE: per value either scalars asked in order or a
table folded by first, average or max, optionally with a pattern for
text answers; memory as total with used or free, or a percentage, in
KiB or bytes; and how to read the interfaces. The application polls
and computes.

HealthMetricsMixin.get_health_metrics now warns that it is deprecated;
it goes in 5.0.

Closes #32

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "napalm-device-types"
-version = "4.11.0"
+version = "4.12.0"
 description = "Abstract device-type base classes for NAPALM drivers"
 readme = "README.md"
 requires-python = ">=3.10"