Cooperative shutdown

Foundation capability (taktora-executor v0.1): the runtime exits cleanly on signal or programmatic stop without leaking worker threads or shared-memory artefacts.

Feature: Cooperative shutdown FEAT_0016
status: open
satisfies: FEAT_0010
is satisfied by: REQ_0050, REQ_0051
is implemented by: BB_0035

The runtime exits cleanly on signal or programmatic stop without leaking worker threads or shared-memory artefacts.
Requirement: Signal-driven shutdown REQ_0050
status: open
satisfies: FEAT_0016

The runtime shall return cleanly from run() when SIGINT or SIGTERM is delivered to the process, surfacing iceoryx2’s WaitSetRunResult Interrupt and TerminationRequest variants.
Requirement: Programmatic shutdown wakeup REQ_0051
status: implemented
satisfies: FEAT_0016
is verified by: TEST_0129
links outgoing: BB_0035, TEST_0129

The runtime shall expose a clonable Stoppable handle whose stop() method wakes the WaitSet thread within a bounded time even when no other trigger is pending.