feat: alternative fingerprint rules count once (4.8.0)

Discovery compares drivers by score divided by the most a driver could
score, and that maximum summed every positive rule. Rules that never
match together, such as one vendor's landing page or another's, made a
driver that knows several vendors lose to one that knows none:
napalm-redfish's Supermicro landing page scored 6 of 41 and lost to a
bare "linux" in the same BMC's SNMP sysDescr, 5 of 18.

FingerprintRule gets an optional group. rules_max_weight() sums the
positive rules and counts each group once, with its strongest rule.
Existing rules have no group and count as before.

napalm_device_types/__init__.py

@@ -60,7 +60,7 @@ Introspection -- :func:`~napalm_device_types.roles.roles_of`,
 :func:`~napalm_device_types.roles.primary_role_of`.
 """
 
-from napalm_device_types.base import DeviceTypeDriver, FingerprintRule, PortSpec
+from napalm_device_types.base import DeviceTypeDriver, FingerprintRule, PortSpec, rules_max_weight
 from napalm_device_types.access_point import AccessPointDriver
 from napalm_device_types.channel import (
     ByteStream,
@@ -156,6 +156,7 @@ __all__ = [
     "DeviceTypeDriver",
     "DhcpServerMixin",
     "FingerprintRule",
+    "rules_max_weight",
     "FirewallDriver",
     "FirewallRuleMixin",
     "HealthMetricsMixin",

napalm_device_types/base.py

@@ -8,6 +8,7 @@ live connection.
 
 from __future__ import annotations
 
+from collections.abc import Iterable
 from typing import NamedTuple
 
 from napalm.base import NetworkDriver
@@ -24,12 +25,36 @@ class FingerprintRule(NamedTuple):
     weight    — evidence added to the driver's score on match
     mandatory — pattern absent → driver immediately disqualified
     negative  — pattern present → weight subtracted instead of added
+    group     — rules sharing a group are alternatives that never match
+                together (one vendor's landing page *or* another's); only the
+                strongest of them counts towards the most a driver can score
     """
 
     pattern: str
     weight: float = 1.0
     mandatory: bool = False
     negative: bool = False
+    group: str | None = None
+
+
+def rules_max_weight(rules: Iterable[FingerprintRule]) -> float:
+    """The most evidence *rules* can add together.
+
+    Every positive rule counts, except that a group of alternatives counts once,
+    with its strongest rule. Discovery divides a driver's score by its maximum to
+    compare drivers; summing alternatives would make a driver that recognises
+    three vendors' pages lose to one that recognises none.
+    """
+    total = 0.0
+    group_best: dict[str, float] = {}
+    for rule in rules:
+        if rule.negative or rule.weight <= 0:
+            continue
+        if rule.group is None:
+            total += rule.weight
+        else:
+            group_best[rule.group] = max(group_best.get(rule.group, 0.0), rule.weight)
+    return total + sum(group_best.values())
 
 
 class PortSpec(NamedTuple):