test(console): add persistent connection stability stress

[regyssilveira]

Investigation of issue #581

Adds a Windows/Delphi stability test aligned with the reported scenario:

• 50 concurrent clients;
• persistent HTTP/1.1 connections with keep-alive;
• 1,500 requests per client;
• 75,000 total transactions;
• connection and read timeouts;
• failure on exceptions, timeouts, non-200 responses, or invalid response bodies;
• reporting of the highest observed latency and the first error.

Local result

Delphi 12/Win32, Horse 3.3.9/current master:

clients=50 requests=75000 delay_ms=0 errors=0 max_latency_ms=1313

The instability was not reproduced on this machine. No production code was changed: the purpose is to provide a deterministic reproduction and allow execution on the reporter's Windows Server 2022 environment before independently isolating the scheduler and socket keep-alive behavior.

The workload can also be paced at approximately 19.2 seconds between requests, matching 75,000 transactions from 50 clients over eight hours.

Refs #581