fix(core): DIAGNOSTICS_FAILURE carries a dead status set and non-1.6 vocabulary

[sepehr-safari]

detectDiagnosticsFailure gates on the same status twice, and the outer gate is
misleading.

DIAGNOSTICS_FAILURE_STATUSES (detection.ts:754) lists five values:

const DIAGNOSTICS_FAILURE_STATUSES = new Set([
  'Idle', 'Uploaded', 'UploadFailed', 'DiagnosisFailed', 'NotImplemented',
]);

but the body then narrows again:

if (status === 'UploadFailed' || status === 'DiagnosisFailed') {

So Idle, Uploaded and NotImplemented sit in a set named "failure statuses"
and can never produce a failure. Confirmed by probing the rule directly: Idle,
Uploading, Uploaded and NotImplemented all report nothing, and only
UploadFailed and DiagnosisFailed fire. The behaviour is correct; the code
says something different from what it does.

Two things worth settling at the same time, both the same family as #154:

• Uploading is a real OCPP 1.6 DiagnosticsStatus value and appears nowhere in
  the rule, not even in the outer set.
• DiagnosisFailed and NotImplemented look like later-generation vocabulary
  rather than OCPP 1.6 DiagnosticsStatus. Worth checking against the
  enumeration the same way bug: FIRMWARE_UPDATE_FAILURE matches statuses outside the OCPP 1.6 enum and misses InstallationFailed #154 checked FirmwareStatus against section 7.25, and
  transcribing the result into a comment as that fix did.

If DiagnosisFailed turns out not to be a 1.6 value, note that
diagnostics-failure.ts uses exactly that status, so the corpus would be
exercising a value no conformant 1.6 station sends. That is the same problem #154
found and fixed for InstallFailed.

No behaviour change is required to remove the dead gate; the vocabulary question
may change behaviour and is worth deciding deliberately.