feat(aws): EventBridge Scheduler schedules + groups

[NitinKumar004]

Summary

Adds the standalone Amazon EventBridge Scheduler control plane as a new AWS surface (wire service `scheduler`, restJson1 verb+path). This is distinct from the existing `eventbridge` service and from GCP Cloud Scheduler (`services/scheduler`); to avoid the directory collision with the latter, the new service lives under `eventbridgescheduler`.

Control-plane only — schedules are never fired at their targets.

Operations

• Schedules: CreateSchedule (POST /schedules/{Name}), GetSchedule, UpdateSchedule (PUT, full replace), DeleteSchedule, ListSchedules — GroupName defaults to `default`.
• Schedule groups: CreateScheduleGroup (POST /schedule-groups/{Name}), GetScheduleGroup, DeleteScheduleGroup (cascades to its schedules), ListScheduleGroups. The `default` group always exists implicitly and cannot be deleted.
• Tags (schedule groups only): TagResource / UntagResource / ListTagsForResource on /tags/{arn}, scoped to `:scheduler:` ARNs.

Drift-free computed fields

• Schedule ARN `arn:aws:scheduler:::schedule//`, group ARN `arn:aws:scheduler:::schedule-group/`, creation/last-modification dates and group ACTIVE state are minted once at create and stored, stable across every read and after update.
• `target` and `flexible_time_window` (plus start/end dates) round-trip verbatim via json.RawMessage passthrough so nested blocks cannot drift.

Architecture

Follows the restJson1 siblings (mq/grafana/aps): 3-layer split (services/driver, providers/aws, server/aws), COW memstore with deep-clone-on-read, Snapshottable, X-Amzn-Errortype exception tagging. Registered before the S3 catch-all; /schedules and /schedule-groups are unique roots and /tags is scoped by `:scheduler:`, disjoint from sibling tag claimants.

Terraform plan-clean e2e

Against `cloudemu serve` with a real `hashicorp/aws` provider (scheduler endpoint override):

• `apply` — aws_scheduler_schedule_group + aws_scheduler_schedule (schedule_expression="rate(1 hour)", flexible_time_window mode=OFF, target arn+role_arn) created with correct computed ARNs.
• `plan -detailed-exitcode` → exit 0, no drift on schedule/group arn, creation_date, state, target and flexible_time_window blocks.
• Update (description + state=DISABLED) applies, then plan-clean again.
• `destroy` → subsequent GET returns 404 ResourceNotFoundException.

SDK round-trip tests (aws-sdk-go-v2/service/scheduler, test-only) assert byte-stable create→get→update→delete.