Function update_file_incremental 

pub fn update_file_incremental(
    index: &mut SemanticIndex,
    project_root: &Path,
    path: &Path,
    content: &str,
) -> IncrementalUpdateResult

Update a single file in an existing SemanticIndex.

This performs an incremental update:

1. Remove all data for the old version of the file (if it exists)
2. Re-extract the file
3. Add the new symbols, tokens, references, scopes
4. Re-resolve edges for the new symbols

This is much faster than rebuilding the entire index (~20-50ms per file).

Arguments

• index - The existing SemanticIndex to update
• project_root - Project root path for computing relative paths
• path - Path to the file to update
• content - New content of the file

Returns

Statistics about the update operation