fix(otel): close spans child first at invocation end

[zhongkechen]

Summary

• close still-open attempt spans before their operation spans
• record operation start order and drain it in reverse during invocation shutdown
• add a regression test covering attempt, child operation, and parent operation timestamp containment

Root cause

InvocationOtelPlugin.onInvocationEnd() previously ended open operation spans by iterating a ConcurrentHashMap. Its iteration order is unspecified, so a parent operation could be ended before a still-open child. This produced child end timestamps a few microseconds later than the parent and failed OTel conformance validation.

The plugin now keeps keyed span access in the concurrent map and records start order in a ConcurrentLinkedDeque. Invocation shutdown closes attempts first, then polls operation IDs from the deque tail so descendants close before ancestors. IDs for operations already completed are skipped when their span is absent from the map.

Impact

Interrupted invocations now export properly nested span timestamps while preserving concurrent keyed access for normal operation lifecycle events.

Validation

• mvn -pl otel-plugin spotless:apply
• mvn -pl otel-plugin test (123 tests passed)
• focused nested-span regression test passed