[Feature] Define the future public SPARQL Query API

[abdessamad-abdoun]

to be implemented later, after the cleanup and decoupling phase

• Users should interact only with the public API classes.
• Users should not depend on the parser, AST, bridge, or KGRAM internals.
• Define the prepared query types: tuple, boolean, graph, and update.
• Define the responsibilities of RepositoryConnection, Query, Operation, Update, and Dataset.
• Replace or hide NextSparqlPipelineExecutor behind this public API.
• Clarify the handling of initial bindings, datasets, timeouts, and error management.