@W-22255905: Add clone sandbox option on VS Code

[amit-kumar8-sf]

Summary

Adds Clone Sandbox and View Clone Details actions to the Realm Explorer sandbox context
menu, with full lifecycle visibility:

• Clone Sandbox — prompts for TTL, target resource profile (medium/large/xlarge/xxlarge,
  or "same as source"), and optional comma-separated notification emails; calls POST /sandboxes/{id}/clones and polls /clones/{cloneId} with a progress notification reporting
  status, progressPercentage, and lastKnownState until COMPLETED / FAILED.
• View Clone Details — only shown when the sandbox has a non-empty clonedFrom; opens GET /sandboxes/{id}?expand=clonedetails as a preview JSON document.
• Source sandbox state — while a Clone Sandbox action is in flight, the source row renders as
  cloning with the clone codicon (warning-yellow) via a client-side tracking flag on
  SandboxTreeDataProvider (markSourceCloning / unmarkSourceCloning), independent of whatever the
  API reports.
• Target sandbox state — a cloned sandbox reported as failed (the API's interim state during
  clone setup) is rendered as setting up with server-process~spin.
• cloning API state — registered in STATE_ICONS and TRANSITIONAL_STATES so realm
  auto-polling continues through it.
• Menu visibility rules — Clone Sandbox only shows for started/stopped sandboxes; Open Business Manager, Extend Expiration, and Delete Sandbox are hidden during cloning / setting up; Start/Stop/Restart match both plain and -cloned context-value variants.
• Post-completion refresh — after COMPLETED / FAILED, the handler keeps the source marked
  and refreshes the realm for 3 additional poll intervals (30s) so the list endpoint has time to
  propagate final states before the cloning label clears, then re-arms startPollingRealm for the
  new target sandbox's transitional states.
• Added clonedFrom and sourceInstanceIdentifier to the SandboxInfo interface.
• Extracted pure display logic into src/sandbox-tree/sandbox-clone-helpers.ts for testability.

Testing

• Added 39 unit tests across two new files:
  • src/test/sandbox-clone-helpers.test.ts — covers getRealmInstanceId,
    getActiveCloneSourceIds (target states, empty strings, missing fields), computeSandboxDisplay
    (all branches: plain, cloned, source, cloned+failed precedence, case normalization), and state-set
    membership.
  • src/test/sandbox-menu.test.ts — loads package.json and asserts visibility contracts for
    every sandbox command against synthetic viewItem context values, including -cloned suffix
    behavior and the hide-during-cloning/settingup rules for Open BM / Extend / Delete.
• All 39 tests pass locally under Mocha TDD; pnpm run typecheck:agent, pnpm run lint:agent, and
  pnpm run pretest all clean.
• Manually exercised against a real realm: triggered Clone on a started sandbox, verified progress
  notification (name on line 1, id + status % on line 2), source row transitioning to cloning,
  target row appearing as setting up, and both rows converging to their final states after clone
  completion.

Dependencies

• No net-new third-party dependencies were added
• If net-new third-party dependencies were added, rationale/discussion is included and
  3pl-approved is set by a maintainer

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• Tests pass (pnpm test)
• Code is formatted (pnpm run format)