Added file handling, type handling, large rework of Classes

[tschwarzl]

Added

• print method to all instantiable classes
• added examples to DTAColumnSpecs, which need to be following a pattern if provided and are mutatially exclusive from values
• introducted colclass, which is a placeholder for further addition for automatic preprocessing efforts
• file handling with classes: DTAFileInfo, DTAFileInfoTabular, DTAFileInfoCSV, DTAFileInfoTSV, DTAFileInfoDelim
• introduced classes DTARule, DTARuleCollection, DTARuleColCondition, DTARuleColRange, DTARuleColUnique for rules
• introducted classes DTADataSetTabular handling tabular data, deriving from DTADataSet
• functions to access slots
• S7 validators for all classes
• introduced DTAColumnSpecStructure and DTAColumnSpecStructureSAS for handling type, format, length of a column spec
• info variables to DTADataSet and DTADataSetTabular
• example factory functions: create_example_DTA(), create_example_DTAColumnSpec(), create_example_DTAColumnSpecCollection(), create_example_DTADataSetTabular(), create_example_DTAFileCSV(), create_example_DTAFileTSV(), create_example_DTAMetaData(), create_example_DTARuleColCondition(), create_example_DTARuleColUnique(), create_example_DTARuleColRange()
• as.list functions to DTAColumnSpecCollection, DTAColumnSpecCollection and DTARules derivates

Changes

• renamed functions to snake_case
• renamed DTAFileInfo to DTAFile
• renamed DTAContainer to DTADataSet
• improved GitHub Action workflows
• reworked data backend to use arrow::Table for better performance and memory usage
• improved vignette and README.md
• improved testthat tests
• improved CLI messages
• moved rules to DTARule and derivate classes
• renamed getter functions to shorter names
• renamed constructor variables
• DTA-class constructor to handle DTAMetaData
• changed container to datasets in class DTA
• moved json schema generation to classes
• removed stored json_schema as it can be dynamically generated