Module execution/runtime/budget

Monotonic execution budget primitive tracking call deadlines and teardown allowances.

Implements the complete-call budget contract (EXEC-001-T07):

Injectable monotonic clock (defaults to performance.now).
Fixed absolute deadline computed once at instantiation.
Distinct execution deadline reserving a finite teardown allowance.
Non-resetting boundary arithmetic (already-expired, exact boundary, repeated checks).
Explicit distinction between host/caller cancellation (ABORTED) and budget expiration (TIMEOUT).
Guaranteed timer cleanup and listener teardown on dispose.
Strict isolation from MCP and transport layers.

Functions