Split sampling rules into typed subclasses

[rubenvanassche]

Summary

• Move sampling rules from an enum-discriminated SamplingRule to an abstract class with one concrete subclass per rule type under src/Sampling/Rules/.
• Add DeferredSamplerRule marker interface so rules that need a resolved handler can opt in. Rename DeferrableSampler::isPending() → isDeferred() and swap the using() / usingDeferred() semantics so using() is the immediate-evaluation form.
• Add SamplingAttributesProvider contract so providers can expose a cheap map (e.g. laravel.route.name) for rule matching, separate from the full toArray() payload that goes into spans.
• Split JobAttributesProvider into QueuedJobAttributesProvider (queue side, no handler info) and JobAttributesProvider extends QueuedJobAttributesProvider, EntryPointHandlerProvider (execution side). CommandAttributesProvider now extends EntryPointHandlerProvider directly. Php* providers carry their own handler info, so the recorder-side defaults disappear from EntryPoint::setHandlerFromAttributesProvider.
• Routing recorder folds the route attributes provider's toArray() into the routing span (parity with command/job).
• SpansRecorder::endSpan short-circuits attribute-closure resolution when neither tracing nor reporting will keep the span.
• Drop the array form of SamplingRule (SamplingRuleType enum + fromArray); rules are constructed directly via the static factories.
• Bump the dev-main alias to 3.x-dev.