manager: Add temporary code to debug issue #7150

[CharlieFenton]

Add temporary debugging code to Manager to:

• show time each RPC request is added to asynchronous RPC queue
• show time each RPC request completes
• RPC causing "Communicating with client" dialog to appear
• all RPCs in queue when the dialog appears
• whether the dialog was dismissed automatically because RPC completed (wxID_OK), user clicked Cancel (wxID_CANCEL) or use clicked "Exit BOINC Manager (wxID_EXIT).

Built on BOINC 8.2.15 rather than master to avoid the possibility that later changes to master might affect the problems reported in issue #7150

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Summary by cubic

Adds compile-time gated debug logging in the Manager to trace async RPCs and diagnose “Communicating with client” stalls. Logs each RPC enqueue/completion with microsecond timestamps and RPC names, prints when the dialog opens/closes with the queue and close reason, logs RPC errors, and adds PRINT_ONLY_DEMAND_RPC_INFO to limit the enqueue/completion logging to demand RPCs.

^{Written for commit d14ce1a. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 1 file

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