fix: validate MaxEntries to prevent infinite loop in DebugEntryStore

[viogustian]

Closes #112

Problem

Setting MaxEntries to a negative value or zero causes an infinite loop
in DebugEntryStore.Add(), because the while condition is always true.

Solution

Added DebugProbeOptionsValidator that validates MaxEntries >= 1
during startup. If the value is invalid, an InvalidOperationException
is thrown immediately with a clear error message.

Testing

• Reproduced the bug with MaxEntries = -1 (app hangs on first request)
• Added two unit tests for zero and negative values
• All 51 tests pass

[georgidhristov]

Tested locally with MaxEntries = 0 and MaxEntries = -1.

The application now fails fast during startup with a clear validation error instead of hanging on the first request.

Thanks for the contribution.