s7contract 0.1.0

• Renamed the primary new_interface() requirement argument to generics; methods remains a compatibility alias.
• Tightened interface and trait requirements to require S7 generics created with S7::new_generic().
• Added optional progressive argument and return checks for interface requirements and trait methods, including with() and %::% evaluation syntax.
• Reworked contract descriptor objects as internal S7 classes throughout.
• Added a Haskell-style Maybe/monad dictionary example to the interface and trait vignette.
• Added CRAN-facing vignettes with number-like, vector-like, and bioinformatics container examples.
• Added CRAN submission comments and metadata updates for vignette building.
• Fixed impl_trait() so failed S7 method registration no longer leaves a stale trait implementation record.
• Preserved explicit NULL associated item values and allowed subtraits to retrieve inherited associated items.
• Added regression tests for trait registration failure and associated metadata edge cases.
• Simplified the README to keep the Go/Rust analogies clearly scoped to runtime S7 helpers.