Update & improve coverage: add mapport tests

[tevio]

Improved Mapport Coverage

mapport: add hook-based seam for PCP/UPnP, expand unit tests, improve coverage; exclude seam header from coverage

Motivation / Context

• The mapport thread manages NAT traversal (PCP/NAT-PMP/UPnP) and historically had limited, flaky coverage because tests could trigger real network I/O and OS firewalls.
• We want deterministic tests that exercise mapport lifecycle and PCP control-flow without opening sockets, and a clean coverage report without noise from glue code.

What’s changed

• Introduced a small, production-compiled hook seam to make network-dependent calls substitutable in tests:
  • New neutral hooks namespace: mapport_hooks with function-pointer variables that default to real implementations.
    • mapport_hooks::QueryDefaultGatewayFn
    • mapport_hooks::PCPRequestPortMapFn
    • mapport_hooks::NATPMPRequestPortMapFn
    • mapport_hooks::GetLocalAddressesFn
  • src/mapport.cpp now invokes these hooks instead of calling the functions directly inside ProcessPCP() and related logic. No behavior change in production: the hooks point to the real functions by default.
• Expanded and hardened unit tests for mapport:
  • Tests exercise thread lifecycle (StartMapPort, InterruptMapPort, StopMapPort), dispatch toggling, idempotent starts, and key branches in ProcessPCP().
  • Tests override the hooks at runtime with stubs (via a small RAII guard) to drive PCP/NAT-PMP paths deterministically without any network traffic or firewall prompts.
  • Tests use the standard BasicTestingSetup fixture for required global initialization.
• Coverage hygiene:
  • Excluded the trivial seam header from LCOV to avoid a spurious 0% row: src/mapport_hooks.h filtered in cmake/script/CoverageInclude.cmake.in.
• CTest/coverage ergonomics (if not already present in your tree):
  • CTest runs with --output-on-failure and explicitly ensures mapport_tests execute during coverage, so unit-test hits always contribute to the HTML reports.

Before

After