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

tests/test_snmp_health_profile.py

@@ -0,0 +1,53 @@
+"""SNMP health: drivers declare data, the application polls (docs/STRUCTURE.md).
+
+``SnmpHealthProfile`` is the shape a driver states its device's OIDs in.
+``HealthMetricsMixin``, which collected in the base package, is deprecated.
+"""
+
+from __future__ import annotations
+
+import asyncio
+from typing import ClassVar, get_type_hints
+
+import pytest
+
+from napalm_device_types import (
+    HealthMetricsMixin,
+    SnmpHealthProfile,
+    SnmpInterfacesSpec,
+    SnmpMemorySpec,
+    SnmpValueSpec,
+)
+
+
+def test_a_profile_says_where_each_value_lives():
+    assert set(get_type_hints(SnmpHealthProfile)) == {"uptime", "cpu", "memory", "interfaces"}
+    assert set(get_type_hints(SnmpValueSpec)) == {"oids", "table", "fold", "pattern"}
+    assert set(get_type_hints(SnmpMemorySpec)) == {"total", "used", "free", "percent", "unit"}
+    assert set(get_type_hints(SnmpInterfacesSpec)) == {"skip", "tx_errors_are_drops"}
+
+
+def test_every_key_is_optional():
+    for spec in (SnmpHealthProfile, SnmpValueSpec, SnmpMemorySpec, SnmpInterfacesSpec):
+        assert spec.__required_keys__ == frozenset(), spec.__name__
+
+
+def test_a_driver_declares_its_profile_as_a_class_attribute():
+    class Driver:
+        SNMP_HEALTH_PROFILE: ClassVar[SnmpHealthProfile] = {
+            "cpu": {"oids": ["1.3.6.1.4.1.9.1", "1.3.6.1.4.1.9.2"]},
+            "memory": {"percent": {"table": "1.3.6.1.4.1.9.3", "fold": "first"}},
+        }
+
+    assert Driver.SNMP_HEALTH_PROFILE["cpu"]["oids"][0] == "1.3.6.1.4.1.9.1"
+
+
+def test_the_collector_in_the_base_package_warns_that_it_is_deprecated():
+    async def get(oid):
+        return None
+
+    async def walk(oid):
+        return {}
+
+    with pytest.warns(DeprecationWarning, match="SNMP_HEALTH_PROFILE"):
+        asyncio.run(HealthMetricsMixin.get_health_metrics(get, walk))