server: visit parent slots before child slots (#30779)
* server: visit parent slots before child slots
A parent slot wakes its waiting child slots once it finishes the shared
prompt prefix, while slots are visited in id order. When a child task
lands on a lower slot id than its parent, the child is visited before
the parent wakes it and waits an extra batch to process its suffix.
Non-child slots are now visited before active child slots, so every
child woken by its parent joins the same batch.
* server: check systemone test events through test tags
The systemone tests matched free-form debug messages, including the
formatted f_keep value of the prompt cache. The server now emits
__TEST_TAG_WAIT_PARENT_SLOT__ when a child slot waits for its parent,
__TEST_TAG_PROMPT_CACHE_RESTORE__ on every prompt cache restore and
__TEST_TAG_PROMPT_CACHE_FULL_RESTORE__ when the whole cached prompt is
a prefix of the new one, compared on token counts.
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Co-authored-by: Pascal <admin@serveurperso.com>