fix: implement periodic peer discovery without connection failure tracking

[diegomrsantos]

Issue Addressed

Fixes peer count plateau and connection denial issues caused by generic discovery attempting to connect to peers without needed subnets.

Proposed Changes

Subnet-Aware Periodic Discovery

• Trigger discovery every 30s when peer count is below target
• Uses subnet filtering via start_subnet_query() instead of generic discover_peers()
• Only discovers and dials peers that offer our needed subnets
• Prevents MissingNeededSubnets connection denials

Connection Metrics

• Track inbound vs outbound connection counts
• Provides visibility into connection direction distribution
• Helps monitor peer connectivity patterns

Logging Improvements

• Connection errors logged at debug level (normal P2P behavior)
• Reduces log noise while maintaining debugging capability
• Increased log retention (5 files vs 1) for better historical tracking

Root Cause Analysis

The original PR #649 added generic discover_peers() which found ANY peers on the network:

1. Discovery finds peer with subnets [1, 2, 3]
2. We need subnets [5, 6, 7]
3. We dial the peer
4. Connection attempt succeeds
5. Connection manager checks if peer offers needed subnets
6. Connection denied with MissingNeededSubnets error
7. Wasted connection attempt, cycle repeats

Solution

Use subnet-aware discovery that filters ENRs before dialing:

1. Discovery filters by our needed subnets [5, 6, 7]
2. Only peers offering these subnets are discovered
3. We dial filtered peers
4. Connection manager checks subnets
5. Connection accepted - peer offers what we need
6. Peer count grows successfully

Additional Info

This PR intentionally excludes the connection failure blacklist mechanism from PR #649 to evaluate a simpler approach.

Two complementary discovery mechanisms:

1. Per-subnet discovery (existing check_subnet_peers): Ensures minimum 6 peers per subnet
2. Overall discovery (new, subnet-aware): Helps reach target peer count by discovering for ALL needed subnets

Comparison with PR #649:

• ✅ Includes: Periodic subnet-aware discovery, connection tracking, logging improvements
• ❌ Excludes: Connection failure tracking, peer blacklisting, memory-bounded failure records
• ✅ Fixes: Connection denial bug from generic discovery

Advantages:

• Simpler implementation with less state management
• No memory overhead for failure tracking
• Avoids potential issues with false-positive blacklisting
• Prevents wasted connection attempts to unsuitable peers
• Focus on proactive subnet-filtered discovery

Trade-offs:

• No automatic avoidance of persistently failing peers
• Relies on discovery to find working peers with correct subnets

[AgeManning]

Looks good to me

[dknopik]

LGTM, thank you!!!