Simplifying SNLPCorpus, added InMemoryCorpus as new comforming type.

Sources/SwiftNLP/0. SNLP Internal Protocols/SNLPCorpus.swift

...NLP/0. SNLP Internal Protocols/SNLPSearchableCorpus.swift

...ction/DictionaryCorpus + RangeReplacableColleection.swift

Sources/SwiftNLP/1. Data Collection/DictionaryCorpus.swift

...NLP/1. Data Collection/DurableHNSWCorpus + Sequence.swift

Sources/SwiftNLP/1. Data Collection/DurableHNSWCorpus.swift

...1. Data Collection/EphemeralHNSWCorpus + Dictionary.swift

...P/1. Data Collection/EphemeralHNSWCorpus + Sequence.swift

...ces/SwiftNLP/1. Data Collection/EphemeralHNSWCorpus.swift

Sources/SwiftNLP/1. Data Collection/InMemoryCorpus.swift

...s/SwiftNLP/1. Data Collection/String + SNLPDataItem.swift

...ests/1. Data Collection/HNSW/DurableHNSWCorpusTests.swift

...ts/1. Data Collection/HNSW/EphemeralHNSWCorpusTests.swift

...s/SwiftNLPTests/2. Encoding/ContextFreeEncoderTests.swift

...iftNLPTests/2. Encoding/NaturalLanguageEncoderTests.swift