List all functions that call a specific target function. Analyzes the call graph to show dependencies.

Use this tool when:

• Assessing refactoring impact (which code will be affected by changes)
• Understanding where a function is used in the codebase
• Tracing execution flow during debugging

Examples:

• Find callers of User.create/1 before modifying its signature
• Identify all code that depends on a helper function before removing it
• Trace which routes call a specific controller action

Returns: List of caller functions with module, name, arity, and file location.