Function classify_context 

pub fn classify_context(before_cursor: &str) -> CompletionContext

Classify the completion context from the text before the cursor.

before_cursor is the slice of the current line up to (and not including) the cursor, already mapped to a byte boundary via offset_to_byte.

This is the LSP classification body, ported verbatim, including the in_code_position-gated Tag/Link detection.