feat(routing): move sticky-key retries into routing policy with lazy attempts

Replace the provider/endpoint max_retries fields as the source of same-key
retries with a routing policy setting, sticky_key_attempts (default 2). Only
the first-ranked candidate is retried on the same key; every failover
candidate gets a single attempt so failover keeps advancing instead of
retrying each fallback key.

Materialize exactly one attempt per candidate and derive same-key retries in
the attempt loop after a candidate-scoped failure, so the retry budget no
longer inflates up-front materialization and needs no upper bound. The budget
travels in the report context; retries reuse the plan with a fresh candidate
id and incremented retry index. Pool groups only retry their first key within
the retry-index stride.

Expose the setting in the routing profile editor and the set_scheduling rule
action, and drop the max_retries input from the provider form.

crates/aether-routing-core/src/lib.rs

@@ -15,7 +15,7 @@ pub use conditions::{RoutingCondition, RoutingConditionContext, RoutingCondition
 pub use model::{
     RoutingDefaultPolicy, RoutingGroupBinding, RoutingGroupBindingSubject, RoutingGroupConfig,
     RoutingGroupRecord, RoutingGroupVersionRecord, RoutingModelPolicy, RoutingPoolPolicyOverride,
-    RoutingRule, RoutingSchedulingPreset,
+    RoutingRule, RoutingSchedulingPreset, DEFAULT_STICKY_KEY_ATTEMPTS,
 };
 pub use mutations::{
     apply_json_patch_operations, validate_header_patch, validate_json_patch_operations,