Fix: DSP edge cases around groups

[maximmaxim345]

This PR fixes various edge cases I missed with #1839.

Reload Detection

The existing logic for issuing DSP reloads when grouping or ungrouping was flawed.
This reworks this section, handling all edge cases I can think of including:

• Don't restart playback if the leader already had DSP disabled
• Don't restart playback if a group shrank to a single device that has DSP disabled
• Proper handling of PlayerGroups
• PlayerGroup with only a single member

Additionally, the existing logic had another oversight where it would issue a reload command for every device in the group. This fixes that by only reloading the leader/PlayerGroup.

PlayerGroups with single members

Another previously missed edge case involves groups with single members that would mistakenly use the DSP Config of the PlayerGroup instead of the Player. This is now fixed.

This now allows all PlayerGroups with single devices to correctly apply DSP.

[marcelveldt]

The linter found something - maybe add an exclusion to that function for now, it complains about too many statements.
Something for later times is trying to split all that up into smaller parts but not a prio for now.