feat: Implement MicroSD Toast Timer configuration (Implements Issue #546)

[securesigner]

This PR connects the existing 'MicroSD Toast Timer' setting to the toast notification logic, resolving #546.

Previously, the toast notification for SD card insertion/removal used a hardcoded 3-second duration regardless of the user setting.

Screenshots omitted as this is a behavior/timing change, not a visual UI change.

This pull request is categorized as a:

• New feature
• Bug fix
• Code refactor
• Documentation
• Other

Checklist

• I’ve run `pytest` and made sure all unit tests pass before submitting the PR

If you modified or added functionality/workflow, did you add new unit tests?

• No, I’m a fool
• Yes
• N/A

I have tested this PR on the following platforms/os:

• Raspberry Pi OS Manual Build
• SeedSigner OS on a Pi0/Pi0W board
• Other (GitHub Codespaces / Linux Container)

Note: Verified functionality manually using a reproduction script to simulate hardware events."
--base dev

[Chaitanya-Keyal]

NACK. Unless I am misinterpreting what this PR aims to do:

Issue #546 was already fully resolved by PR #600. That introduced the three MicroSD toast timer options (Disabled / 5 seconds / Until SD removed) and properly connected them to the boot-time RemoveSDCardToastManagerThread via the controller's startup logic:

seedsigner/src/seedsigner/controller.py

Lines 294 to 297 in bdcc7c2

	if self.settings.get_value(SettingsConstants.SETTING__MICROSD_TOAST_TIMER) == SettingsConstants.MICROSD_TOAST_TIMER_FIVE_SECONDS:
	self.activate_toast(RemoveSDCardToastManagerThread())
	elif self.settings.get_value(SettingsConstants.SETTING__MICROSD_TOAST_TIMER) == SettingsConstants.MICROSD_TOAST_TIMER_FOREVER:
	next_destination = Destination(RemoveMicroSDWarningView)

This PR modifies SDCardStateChangeToastManagerThread, which is an entirely different toast. That notification was never part of Issue #546's scope.