guard and with_nack first-class CML events

[lePereT]

What type of PR is this? (check all applicable)

• 🍕 Feature
• 🧑‍💻 Code Refactor
• ✅ Test

Description

Converts the operation layer to first-class CML events and simplifies dependants.

Key changes:

• fibers.op: reworked around an Event type with primitive leaves, choice, guard, with_nack, and wrap. Adds poll() and perform_alt(); introduces a compiled synchronisation path and correct nack signalling for losing arms. Exposes new_cond() as a one-shot signal-all primitive.
• fibers.cond: reduced to a thin wrapper over op.new_cond() (one-shot, signal-all semantics).
• fibers.waitgroup: now uses op.new_cond() directly; simplified wait_op() blocking.
• Tests: replaces tests/test_op.lua with comprehensive coverage of base ops, choices, wraps, guards, with_nack (including nested cases), poll(), and perform_alt().

This passes the full test suite.

Related Issues, Tickets & Documents

None.

Screenshots/Recordings

Not applicable.

Manual test

• yes

Manual test description

Ran the full suite locally; exercised new op behaviours (guards, nacks, poll) and confirmed expected outcomes.

Added tests?

• yes

Added to documentation?

• no documentation needed

[optional] Are there any post-deployment tasks we need to perform?

None.