chore: Replace Bluebird promises with native promises

[Amitkahlon]

#33032

Additional details

Steps to test

How has the user experience changed?

PR Tasks

• Have tests been added/updated?
• Has a PR for user-facing changes been opened in cypress-documentation?
• Have API changes been updated in the type definitions?

---

Note

Removes Bluebird and migrates async flows to native Promises/async‑await across CLI, server, fixtures, saved state, and tests.

• Core/Server:
  • packages/server/lib/cypress.ts: replace Promise.try with Promise.resolve().then(...); retain promise-based runElectron; no behavior change intended.
• Fixtures:
  • packages/server/lib/fixture.ts: remove Bluebird; replace Bluebird.delay with setTimeout via native Promise; keep async APIs intact.
• Saved State:
  • packages/server/lib/saved_state.ts: convert formStatePath to async and use fs-extra.pathExists; adjust returns to Promise types; keep create() API, wrapping set with allowed-key normalization.
• CLI:
  • cli/lib/exec/spawn.ts: replace new Bluebird(...) with new Promise(...) in spawn wrapper.
• Tests:
  • packages/server/test/unit/modes/interactive_spec.js: update setup to await savedState.create() in beforeEach.

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[Amitkahlon]

@jennifer-shehane I would like to add more changes, Could you please provide me with some feedback for what I did already?

[jennifer-shehane]

@Amitkahlon Going to kick off tests

[jennifer-shehane]

Thanks!

[alexsch01]

The spacing/indentation changes should be reverted

[jennifer-shehane]

@alexsch01 Yah a bit weird that wasn't surfaced by linting. Addressed here: e656950