Refactor: Migrate email routine sync.Map to pkg/cache

[roguepikachu]

Is your feature request related to a problem? Please describe.
The email provider keeps send-state in a process-local sync.Map (emailRoutine) in both:

• pkg/providers/email/email.go
• pkg/providers/legacy/email/email.go

That map tracks per-id states such as initializing / sending / success / error so a reconcile can avoid starting a second send for the same email id. After StepStatusCache (#239 / #240) and the HTTP rate limiter (#247 / #249) moved onto github.com/kubevela/pkg/cache, this remaining sync.Map should use the same shared cache package for consistency.

Describe the solution you'd like
Migrate emailRoutine to github.com/kubevela/pkg/cache in both email packages:

• Replace sync.Map with the shared cache API (Get / Put / Delete).
• Preserve send-once semantics: do not use a short TTL that can drop in-flight or recently-sent ids and cause duplicate emails. Prefer explicit Delete on completion / failure, or a TTL that is safely longer than any realistic send window only if still correct.
• Keep public email provider behavior unchanged.
• Add or extend unit tests for both non-legacy and legacy paths covering initializing / sending / success / error and no double-send.

Depends on a released github.com/kubevela/pkg version that includes the cache package used by #240 / #249.

Describe alternatives you've considered

• Keep sync.Map indefinitely. Works today, but leaves another bespoke store outside the shared cache direction.
• Use entry-count LRU with aggressive eviction. Rejected unless keys stay pinned for the full send lifetime; eviction must not cause duplicate sends.

Additional context

• Related: Replace StepStatusCache sync.Map with Cache from kubevela/pkg #239 / Refactor: Use generalized cache for StepStatusCache. #240 (StepStatusCache), Refactor: Use generalized LRU cache for HTTP provider rate limiter #247 / Refactor: Use generalized LRU cache for rate limiter cache. #249 (HTTP rate limiter), Introduce cache package pkg#130 / Chore(deps): bump github.com/containerd/containerd from 1.6.12 to 1.6.18 #136 / Chore: refactor suspend step and add op.#Suspend #138.
• Sibling migrations: optional in-memory context storage, workflow memory context store, CUE compat alignment.
• Good first issue: localized to the email provider packages; main risk to watch is duplicate sends under TTL/eviction.