…contexts

The invoke and return contexts emitted by bugc now include
declaration source ranges (pointing to the function definition)
and named argument pointers (using parameter names from the
function signature). This enriches debug info so debuggers can
link call stack entries to source declarations and display
meaningful parameter names.

Changes:
- Add loc/sourceId fields to Ir.Function, populated during
  IR generation from AST function declarations
- Thread module.functions map through EVM codegen so call
  terminators can look up target function metadata
- Build declaration source ranges on invoke contexts (caller
  JUMP, callee entry JUMPDEST) and return contexts
  (continuation JUMPDEST)
- Add parameter names to argument group pointers
- Update call-contexts tests for new fields