Update in Settings and FunctionGenerator

[drslebedev]

This PR includes 3 commits.

Commit 1

Settings refactoring: use CtxSettings, remove BasicSettings

Commit 2

Updates in CtxSettings including:

• Prepare CtxSettings for use with the FunctionGenerator
• Add an additional test case related to CtxSettings.
• Note that parameters modified through the Tag are not persistent across context switches.
• Only user-provided parameters are stored in storedParameters.
• When activateContext() is called, only the parameters explicitly provided by the user are updated; any parameters not included in storedParameters remain unchanged.
• Introduce a setStaged() method to allow parameter adjustments via messages. These staged parameters are not persistent across context switches.
• Introduce expiry time for stored parameters.
• removeExpiredParameters is executed as a last step of Settings::set() call.

Commit 3

Change FunctionGenerator to use CtxSettings to switch between parameter sets.

There are still some dead-lock in qa_Scheduler test for emcc Debug configuration. It happens in "blocking scheduler" test (`qa_Scheduler: Lines 663-697)