[laurentiu021]

System Report's "System log problems (last 7 days)" read the 500 newest critical and error events of the week and
stopped. One noisy source can log 500 errors in a day or two, so a critical event from earlier in the week, an
unexpected shutdown for one, was never read, and the noisy one read "500 times" whatever its real count. And the
report learned how its read went from LastOutcome on an EventLogService that System Report and About share
through one SystemReportService, so one report's read could reset or set the other's result.

What changed

• EventLogService.TallyAsync counts every record of the asked severities in the window, grouped by source and event
  ID, and reads no message: formatting the message is the slow part of a record, and a count needs only the source,
  ID, level and time. On my PC, counting a week of the System log took 0.32 to 0.40 seconds over three runs, against
  the report's 15-second budget.
• It reads 256 records per hop to the thread pool and checks the cancel between batches. A fault ends it as
  Unavailable with no groups, as the Logs tab's read ends, so a read cut short is never listed as the whole week.
• The outcome comes back with the groups, and the report no longer reads LastOutcome.
• SummarizeProblems takes the groups. The report still carries no event message ([Bug]: About / System Report — the exported report carries the machine's MAC address and local IP, undisclosed, in all three formats #2352); a test pins that neither
  record the count builds has one.
• CHANGELOG 1.130.55, README (System Report), ARCHITECTURE (EventLogService, SystemReportService).

Tests

• 600 errors of one source and an older critical event: both counted, 600 and 1.
• A log that ends on a batch boundary, the severity filter, a group's newest time and its critical flag.
• A fault returns no groups and Unavailable; a cancel throws within one batch, against a source long enough that
  only the cancel can end it.
• TallyAsync on a missing log returns LogNotFound and leaves LastOutcome at Ok.
• Integration: a week of the real System log counted inside the report's budget.

Each test failed against the defect it pins: with the count stopped at 500 (the 600-error, batch-boundary and cancel
tests), with every severity counted, a group critical only by its last record, the first record taken as the newest,
a fault returning what was counted, the cancel ignored, the outcome written to LastOutcome, and a full batch taken
as the end of the log.

Closes #2827.