refactor(neon_framework): Replace direct Blocs access with BehaviorSubjects

[provokateurin]

This makes testing easier because no mock blocs need to be created just to pass the subjects along. Also reduces chance of mixing up business logic or making mistakes.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 27.27273% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 28.93%. Comparing base (f0f706e) to head (d4be81f). Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2020   +/-   ##
=======================================
  Coverage   28.93%   28.93%           
=======================================
  Files         250      250           
  Lines       84419    84419           
=======================================
  Hits        24430    24430           
  Misses      59989    59989           

Flag	Coverage Δ		*Carryforward flag
dynamite	31.00% <ø> (ø)		Carriedforward from 21a1852
dynamite_end_to_end_test	61.47% <ø> (ø)		Carriedforward from 21a1852
dynamite_runtime	85.40% <ø> (ø)		Carriedforward from 21a1852
neon_dashboard	92.56% <ø> (ø)
neon_framework	38.30% <27.27%> (ø)
neon_talk	96.31% <ø> (ø)
nextcloud	25.68% <ø> (ø)		Carriedforward from 21a1852
sort_box	90.90% <ø> (ø)		Carriedforward from 21a1852

*This pull request uses carry forward flags. Click here to find out more.

Files	Coverage Δ
...neon_framework/lib/src/blocs/maintenance_mode.dart	76.92% <ø> (ø)
...s/neon_framework/lib/src/blocs/unified_search.dart	100.00% <100.00%> (ø)
...s/neon_framework/lib/src/blocs/weather_status.dart	100.00% <ø> (ø)
...ckages/neon_framework/lib/src/blocs/next_push.dart	0.00% <0.00%> (ø)
...ackages/neon_framework/lib/src/blocs/accounts.dart	0.00% <0.00%> (ø)
packages/neon_framework/lib/src/blocs/apps.dart	0.00% <0.00%> (ø)

[provokateurin]

Oops something in this change causes a stackoverflow...