Felix/refactor

[fan-zhang-sv]

Summary

• Refactors provider + signer request instrumentation into HOFs (withMeasurement, withSignerMeasurement).
• Adds ephemeral isolation via per-instance store (createStoreInstance / createStoreHelpers) and threads store instances into signer/key manager.
• Cleans up EphemeralSigner by inheriting from Signer with minimal overrides and an isEphemeral getter.

Key changes

• Provider instrumentation: BaseAccountProvider and EphemeralBaseAccountProvider now wrap request with withMeasurement (provider owns correlationId create/delete).
• Signer instrumentation: Signer / EphemeralSigner now use withSignerMeasurement (signer reads correlationId only). Uses getter-based options so isEphemeral is evaluated at call time.
• Isolation: createStoreInstance({ persist: false }) enables ephemeral SDK instances that don’t touch global persisted state.
• Key management: SCWKeyManager now takes a StoreInstance and uses createStoreHelpers.

Notes

• Correlation IDs remain scoped to a single request lifecycle: provider creates/cleans up; signer just consumes.