fix: allow getMockImplementation to return "once" implementation

[chaptergy]

Description

Adds a method to get the mock implementation including implementations, which are temporary and created with mock...Once.
Fixes #7030.

A new method was added in order to remain backwards compatible. If this is not desired, it can be replaced.

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. If the feature is substantial or introduces breaking changes without a discussion, PR might be closed.
• Ideally, include a test that fails without this PR but passes with it.
• Please, don't make changes to pnpm-lock.yaml unless you introduce a new test example.

Tests

• Run the tests with pnpm test:ci.

Documentation

• If you introduce new functionality, document it. You can run documentation with pnpm run docs command.

Changesets

• Changes in changelog are generated from PR name. Please, make sure that it explains your changes in an understandable manner. Please, prefix changeset messages with feat:, fix:, perf:, docs:, or chore:.

[netlify]

✅ Deploy Preview for vitest-dev ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	8cf9559
🔍 Latest deploy log	https://app.netlify.com/sites/vitest-dev/deploys/6751cd3b3bc9880008dd5194
😎 Deploy Preview	https://deploy-preview-7033--vitest-dev.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[netlify]

✅ Deploy Preview for vitest-dev ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	6979eb3
🔍 Latest deploy log	https://app.netlify.com/sites/vitest-dev/deploys/677bd1ff8107ed00086bb44f
😎 Deploy Preview	https://deploy-preview-7033--vitest-dev.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[sheremet-va]

We don't need a new method for this. The old one should return the current implementation

[chaptergy]

@sheremet-va Sorry for the delay. I have removed the getNextMockImplementation() and have instead overwritten the getMockImplementation() logic.

[hi-ogawa]

Thanks!