Inline single-use load_extension_input and read_line_dynamic

[python-processing-unit]

Problem

src/main.c:72 defines load_extension_input as a one-liner wrapper with exactly 1 caller at line 343. src/main.c:97 defines read_line_dynamic with exactly 1 caller at line 226. Both add zero abstraction.

Fix

Inline the call to extensions_load_library at line 343 and inline the read_line_dynamic logic at line 226.

Reported by Kilo Code (automated audit tool), not a human reviewer.