Hotfix/small enhancements

[denis-peshkov]

• EdiEngine.Samples: project with examples (210, 322, 810, 850, 997); Common.WriteTransToJson/WriteTransToXml.
• M_210: added L_SPO loop to map.
• M_602: fixed MS segment reference.
• Removed simplified test maps (M_940, M_001) from EdiEngine.Tests.
• Composite tests now use M_850 from EdiStandards with 850.Composite.SLN.OK test data.
• Replaced SegmentDefinitions with EdiEngine.Standards.X12_004010.Segments in tests.
• TargetFrameworks normalized to net6.0, net7.0 and net8.0 in project files.
• README: badges, improved installation section.
• XmlDataWriter: null-safe when batch has no envelope; InvariantCulture for numbers/dates in XML.
• Control segments and AckBuilder: InvariantCulture for numbers/dates (no NNBSP); time format "hhmm" unchanged.
• Tests: NonPrintableCharactersTests (EDI/XML/JSON free of non-printable chars); Xml/JsonReadWrite round-trip assertions.
• Build: duplicate props removed from .csproj (use Directory.Build.props); .csproj UTF-8 BOM.