fix: use procref for FPI procedure roots

[huklaa]

Advances #122 by removing runtime string formatting for the get_count procedure digest in the runnable Rust FPI example.

• uses procref.counter_contract::get_count in reader_script.masm
• links the counter module into the same CodeBuilder chain as the count-reader module
• removes the extra component compilation and manual procedure-root lookup from counter_contract_fpi.rs

This keeps account-id substitution unchanged while letting MASM resolve the procedure root directly from the linked module.