Increase max OID values limit from 1,000 to 50,000

Fixes discovery failures on enterprise network devices with many
interfaces and routing table entries.

Issue:
Discovery was failing with "too_many_oids - OID values map exceeds
1000 entries" on SNMPv3 devices. Enterprise routers/switches during
discovery can easily return 10k-50k OIDs from:
- 100+ interfaces with 20-30 OIDs each
- System info, routing tables, ARP tables, neighbor tables
- Various MIB objects

The original limit of 1,000 was too restrictive for real-world devices
while still being intended as DoS protection.

Changes:
- Increase @max_oid_values from 1,000 to 50,000
- Update test to generate 50,100 OIDs (exceeds new limit)
- Add comment explaining why limit is set to 50k

This maintains DoS protection (prevents multi-million OID attacks)
while accommodating realistic device discovery scenarios.

All tests passing (5578 tests, 0 failures).

lib/towerops/agent/validator.ex

@@ -60,7 +60,8 @@ defmodule Towerops.Agent.Validator do
 
   # Collection limits (prevent DoS via large batches)
   @max_metrics_per_batch 10_000
-  @max_oid_values 1_000
+  # Discovery on enterprise devices can return 10k-50k OIDs (interfaces, routing tables, etc.)
+  @max_oid_values 50_000
   @max_mikrotik_sentences 1_000
   @max_capabilities 20
 

test/towerops/agent/validator_test.exs

@@ -365,8 +365,8 @@ defmodule Towerops.Agent.ValidatorTest do
     end
 
     test "rejects too many OID values" do
-      # Create map with more than max allowed OIDs
-      oid_values = Map.new(1..1100, fn i -> {"1.3.6.1.#{i}", "value"} end)
+      # Create map with more than max allowed OIDs (max is 50_000)
+      oid_values = Map.new(1..50_100, fn i -> {"1.3.6.1.#{i}", "value"} end)
 
       result = %SnmpResult{
         device_id: "550e8400-e29b-41d4-a716-446655440000",