(chore) Migrate /datetime to vitest pt3 - sinon mocks conversion

[cameronjoyner]

FLUP to (chore) Migrate /datetime to vitest pt2 - vitest usage
Similar to [chore]: Replace sinon with vitest in core tests

What this accomplishes

Converts sinon mocks to vitest standard

Note

This only converts assert to expect where absolutely necessary. Otherwise thats coming in a FLUP PR.

Next steps

1. Convert assertions: assert to expect
2. Update test descriptions to BDD-style "should..."
3. Migrate individual tests from Enzyme to RTL (one at a time)

[changelog-app]

Generate changelog in packages/datetime/changelog/@unreleased

Type (Select exactly one)

• Feature (Adding new functionality)
• Improvement (Improving existing functionality)
• Fix (Fixing an issue with existing functionality)
• Break (Creating a new major version by breaking public APIs)
• Deprecation (Removing functionality in a non-breaking way)
• Migration (Automatically moving data/functionality to a new system)

Description

(chore) Migrate /datetime to vitest pt3 - sinon mocks conversion

Check the box to generate changelog(s)

• Generate changelog entry

[svc-palantir-github]

scaffolding

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This is an automated comment from the deploy-preview CircleCI job.

[svc-palantir-github]

Merge branch 'cj/datetime-vitest-2' into cj/datetime-vitest-3

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This is an automated comment from the deploy-preview CircleCI job.

[svc-palantir-github]

formatting

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This is an automated comment from the deploy-preview CircleCI job.

[svc-palantir-github]

adding type MockInstance,

Build artifact links for this commit: documentation | landing | table | demo

This is an automated comment from the deploy-preview CircleCI job.