Remove deprecated field from Discovery

[jmwample]

Description

Remove deprecated element of discovery which has been moved to a different place in the configuration structure.

The network_compatibility information was moved into the system_configuration structure over a year ago and is no longer referenced in the code.
Network compatibility added (merged 3/6/25): 32f1974
Network compatibility moved to system_configuration (merged 4/2/25): 470012f

I believe there should be no clients old enough that this could be a breaking change.

Checklist:

• Remove deprecated network_compatibility field from discovery.

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This change is 

Summary by CodeRabbit

• Refactor
  • Reorganized discovery endpoint response structure and consolidated system configuration settings.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR consolidates network version compatibility management in the VPN discovery API response by removing the redundant network_compatibility field and relying on existing version thresholds in system_configuration.min_supported_app_versions. The Rust struct, all discovery configuration files, and test fixtures are updated consistently.

Changes

Network Compatibility Field Consolidation

Layer / File(s)	Summary
Discovery response contract update nym-vpn-core/crates/nym-vpn-api-client/src/response.rs	NymWellknownDiscoveryItemResponse removes the network_compatibility optional field and keeps feature_flags, system_messages, and system_configuration fields.
Network configuration updates nym-vpn-core/crates/nym-vpn-network-config/default/canary_discovery.json, nym-vpn-core/crates/nym-vpn-network-config/default/mainnet_discovery.json, nym-vpn-core/crates/nym-vpn-network-config/default/sandbox_discovery.json	All three discovery configuration files remove their top-level network_compatibility blocks. Mainnet also adds a statistics_api URL field to system_configuration.
Test fixture alignment nym-vpn-core/crates/nym-vpn-network-config/src/discovery.rs	The test_parse_discovery_response JSON fixture is updated to remove the network_compatibility field from the embedded response data.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A hop, a skip through fields so clean,
Network compat fields no longer seen!
Consolidate we do with care,
Three config files, now light as air.
Version thresholds unified,
In system_configuration they'll reside! 🎉

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Remove deprecated field from Discovery' accurately summarizes the main change—removing the deprecated network_compatibility field from the discovery endpoint.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The pull request description is mostly complete and follows the template structure with a clear description of changes and context.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch jmwample/net-compat

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud