Darling's deadlock maintenance logs a line when a stage recovers after a failed pass (#5634)

[erikdarlingdata]

Darling's hourly PostgreSQL deadlock maintenance logs a warning when one of its stages fails a pass, but logged nothing when a later pass of that stage succeeded. An operator who read the warning had no line saying the stage came back. A stage that succeeds after one or more failed passes now logs one information line that names the stage and how many passes had failed. A clean pass with no earlier failure logs nothing new, and the back-off, skip and progress logic are unchanged.

SECTION: Fixed
ENTRY: - Darling's deadlock maintenance logs a line when a stage recovers after a failed pass ([#5637]) - The hourly PostgreSQL deadlock maintenance logged a warning each time one of its stages failed a pass, but nothing when a later pass succeeded, so the last line an operator saw for the stage was the failure. A stage that succeeds after one or more failed passes now logs one information line naming the stage and how many passes had failed. A clean pass with no earlier failure logs nothing new.

Details

• Darling/PerformanceMonitor.Darling.Service/PgDeadlockRemask.cs, where a clean page resets ConsecutiveFailures: when the count is above 0, one LogInformation line says the stage recovered. It also says how many earlier passes in a row had failed. The line carries the stage name and the count only, never row content.
• Darling/Darling.Tests/PgDeadlockRemaskTests.cs: two live tests on a local test PostgreSQL. AStageThatRecoversAfterFailures_LogsOneRecoveryLine_WithTheFailureCount fails the alert stage twice by renaming its table away. It then restores the table and expects exactly one recovery line for that stage with the count 2. The two other alert-table stages fail and recover on their own, and each is checked to log at most one line. ACleanPassWithNoEarlierFailure_LogsNoRecoveryLine runs the stages with no failure and expects no recovery line. The test logger now also keeps the information lines.
• RED: with the production lines reverted, the first test fails ("The collection did not contain any matching items") and the second passes. With them restored, both pass.
• CHANGELOG.md and docs/changelog/3.10.md carry the entry under 3.10.0 Fixed.

Tests

Darling.Tests on a local PostgreSQL: PgDeadlockRemaskTests Total 26, Failed 0. Then as Total/Failed: *Census* 500/0, *Ratchet* 15/0, *Hygiene* 90/0, *Scrub* 123/0, *Guard* 365/0, *DocComment* 78/0, Stage=Guard 1474/0. 0 build warnings.

Fixes #5634