Refactor FXIOS-9050 [Multi-window] Throttler utility updates

[mattreaganmozilla]

📜 Tickets

Jira ticket
Github issue

💡 Description

Minor adjustments to our Throttler to ensure that rapid consecutive calls will not prevent code from ever being called (it should be called at most once per N seconds). Updates related unit tests.

📝 Checklist

You have to check all boxes before merging

• Filled in the above information (tickets numbers and description of your work)
• Updated the PR name to follow our PR naming guidelines
• Wrote unit tests and/or ensured the tests suite is passing
• When working on UI, I checked and implemented accessibility (minimum Dynamic Text and VoiceOver)
• If needed, I updated documentation / comments for complex code and public methods
• If needed, added a backport comment (example @Mergifyio backport release/v120)

[mobiletest-ci-bot]

	Messages
📖	Project coverage: 32.66%
📖	Edited 3 files
📖	Created 0 files

Client.app: Coverage: 31.28

File	Coverage
Throttler.swift	91.67%	✅
WindowTabsSyncCoordinator.swift	91.18%	✅

Generated by 🚫 Danger Swift against b41d516

[mattreaganmozilla]

cc @OrlaM @nbhasin2 Going to merge this but wanted to get your eyes on it if you have a moment. LMK if any concerns etc., I'm happy to revisit anything or open a follow-up PR.