fix(octopus): review follow-ups for #4849, #4850 and #4852

[mgazza]

Follow-ups to #4849, #4850 and #4852. All three merged quickly — thank you — but these landed on the branches just after the merges, so they need a fresh PR.

1. fix(octopus): stop offering Weekend Happy Hours as available to join — @gcoan's request on #4851:

The BottlecapDave integration has (in v19.0.1) decided to NOT pass through these zero valued events in the power down sensor since they cannot be joined by API. […] suggest we take the same approach of excluding them from available events.

Now that eventType is being requested (#4852) these are identifiable precisely, so Octopus Direct can match BCD. Listing them only produces the join attempts the API rejects (#4593/#4595) and fills the join selector with options that cannot be selected.

Ordering trap worth a reviewer's eye, because it is invisible in the diff. The reward/code/type lookup maps are built from the same events list, and a joined Happy Hour reads its type out of those maps. Skipping before they are populated leaves the joined event with event_type: None and the injected default reward — so a free hour is priced as an 80p/kWh saving session, which is worse than the bug #4852 fixed. The skip therefore sits after the maps are filled, and test_octopus_saving_event_type fails if it is moved above them.

2. style(kraken): use the Kraken: log prefix — Copilot on #4850. The new backoff and token-request warnings read Warn: Kraken token … while the rest of the component uses Warn: Kraken: …; the odd one out breaks grep and log parsing on the usual prefix.

3. docs(octopus): test list numbering and docstring phrasing — Copilot on #4849. The test docstring skipped Test 7 → Test 9 despite Test 8 existing, and "block_count'th" read awkwardly. Note the docstring moved to utils.py in #4850, so the fix is applied there.

Copilot's third point on #4849 was that the PR description undercounted the tests — that was a description issue on a now-merged PR, so there is nothing to change in the code.

Tests

New test_octopus_saving_event_type, registered in unit_test.py:

• a Happy Hour the account was allocated is withheld from available_events but still reaches joined_events carrying event_type: WEEKEND_HAPPY_HOUR
• a TURN_DOWN alongside it is still offered, with its type
• an event with no eventType is unaffected

unit_test.py -k octopus (72), -k saving and -k kraken all pass.