fix: virtualised member list for reassign

[sean-brydon]

Needs design sign off also.

What does this PR do?

Fixes: CAL-4638

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. If N/A, write N/A here and check the checkbox.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

• Are there environment variables that should be set?
• What are the minimal test data to have?
• What is expected (happy path) to have (input and output)?
• Any other important info that could help to test that PR

Checklist

• I haven't read the contributing guide
• My code doesn't follow the style guidelines of this project
• I haven't commented my code, particularly in hard-to-understand areas
• I haven't checked if my changes generate no new warnings

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2 Skipped Deployments

Name	Status	Preview	Comments	Updated (UTC)
cal	⬜️ Ignored (Inspect)	Visit Preview		Oct 29, 2024 3:52pm
calcom-web-canary	⬜️ Ignored (Inspect)	Visit Preview		Oct 29, 2024 3:52pm

[linear]

CAL-4638 Reassign: dropdown slow

[sean-brydon]

Moved to packages/lib

[graphite-app]

Graphite Automations

"Add consumer team as reviewer" took an action on this PR • (10/29/24)

1 reviewer was added to this PR based on Keith Williams's automation.

"Add ready-for-e2e label" took an action on this PR • (10/29/24)

1 label was added to this PR based on Keith Williams's automation.

[CarinaWolli]

Works great, I think design looks good as well 👍

[github-actions]

E2E results are ready!

• Workflow #36401.1 latest results