Adjustments lifecycle, logs + cvar, new tests

[wilianmaique]

• Adjustments to the module lifecycle during mapchange and unload to prevent crashes with ongoing requests.
• Secure cleanup of old requests, callbacks, and forgotten EasyHttp instances after map change.
• Extra protection against incorrect reuse of RequestId after mapchange.
• Correction in ContainerWithHandles for handle generation/reuse.
• Addition of TraceLog for module debugging.
• Addition of the cvar ezhttp_trace_log to turn tracing on or off. The trace is recorded in addons/amxmodx/logs/ezhttp_trace.log.
• Addition of the test amxx_test/scripting/ez_http_mapchange_test.sma.
• Adjustment to the mapchange test to execute changelevel asynchronously.
• Adjustment to the test to prevent the map from continuously restarting when the suite ends.