NRT clean-up after all NRT pull requests got merged

[axunonb]

• ISerializer.SerializationContextis not nullable
• SerializerBase.SerializationContext: Ensure it is initialized and non-null by design
• ServiceProvider.GetService(...) returns a non-null instance or throws an exception if the service is unavailable.
• EncodingProvider.DecoderDelegate throws for invalid encoding argument
• EncoderDelegate GetEncoderFor throws for invalid encoding argument
• SimpleDeserializer: Ensure that ParseContentLine(context, contentLineString).Vaue is a string
• Remove unneccessary conditional access qualifier according to nullable reference types' annotations
• Other small fixes in ical.net
• Small fixes n ical.net.tests
• NRT warninga left are with target nestandard2.0

Unit tests untouched except for those with nullable enable

[codecov]

Codecov Report

Attention: Patch coverage is 51.68539% with 43 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
Ical.Net/Serialization/SerializerBase.cs	36%	9 Missing ⚠️
Ical.Net/Serialization/SimpleDeserializer.cs	40%	3 Missing and 3 partials ⚠️
Ical.Net/ServiceProvider.cs	17%	4 Missing and 1 partial ⚠️
...l.Net/Serialization/DataTypes/TriggerSerializer.cs	50%	2 Missing and 1 partial ⚠️
Ical.Net/CalendarCollection.cs	0%	2 Missing ⚠️
...alization/DataTypes/EncodableDataTypeSerializer.cs	67%	2 Missing ⚠️
Ical.Net/Serialization/DataTypes/EnumSerializer.cs	0%	2 Missing ⚠️
...l.Net/Serialization/DataTypes/IntegerSerializer.cs	0%	0 Missing and 2 partials ⚠️
...Serialization/DataTypes/RequestStatusSerializer.cs	33%	2 Missing ⚠️
Ical.Net/Serialization/DataTypes/UriSerializer.cs	0%	1 Missing and 1 partial ⚠️
... and 7 more

❌ Your patch status has failed because the patch coverage (52%) is below the target coverage (80%). You can increase the patch coverage or adjust the target coverage.
❌ Your project status has failed because the head coverage (66%) is below the target coverage (80%). You can increase the head coverage or adjust the target coverage.

@@         Coverage Diff         @@
##           main   #778   +/-   ##
===================================
  Coverage    66%    66%           
===================================
  Files       105    105           
  Lines      4431   4427    -4     
  Branches   1113   1076   -37     
===================================
+ Hits       2910   2922   +12     
- Misses     1058   1059    +1     
+ Partials    463    446   -17     

Files with missing lines	Coverage Δ
Ical.Net/Calendar.cs	73% <100%> (+1%)	⬆️
Ical.Net/CalendarComponents/VTimeZone.cs	73% <100%> (+1%)	⬆️
Ical.Net/DataTypes/Attachment.cs	78% <100%> (ø)
Ical.Net/DataTypes/PeriodList.cs	87% <100%> (+4%)	⬆️
Ical.Net/Evaluation/RecurrencePatternEvaluator.cs	91% <100%> (ø)
Ical.Net/Serialization/ComponentSerializer.cs	52% <100%> (ø)
....Net/Serialization/DataTypes/DataTypeSerializer.cs	71% <100%> (ø)
....Net/Serialization/DataTypes/DateTimeSerializer.cs	85% <100%> (+2%)	⬆️
...al.Net/Serialization/DataTypes/PeriodSerializer.cs	78% <100%> (+2%)	⬆️
Ical.Net/Serialization/EncodingProvider.cs	100% <100%> (+4%)	⬆️
... and 18 more

... and 1 file with indirect coverage changes

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[minichma]

Wow, -37 branches, -17 partials, +12 hits - very nice! Will try to find time for a review later this week, ideally this evening.

[axunonb]

Thanks for the quick review!