Stack Buffer Overflow in nastran-g.c when processing large PBAR/PSHELL PIDs

**Bug Type:** Security / Buffer Overflow / Crash **Description:** In `src/conv/nastran-g.c`, the PBAR and PSHELL conversion loops use `sprintf` to write group names into a fixed-size stack buffer: ```c char name[NAMESIZE+1]; // 17 bytes sprintf(name, "pbar_group.%d", pbp->pid); sprintf(name, "pshell.%d", psh->pid); ``` If the PID has more than 6 digits (or 10 digits for 32-bit max int), the resulting string exceeds the buffer size, causing a stack buffer overflow. This can crash nastran-g and theoretically allow code execution. ### Proposed Fix: Increase the buffer size to 32 bytes: ```c char name[32]; ``` Use snprintf instead of sprintf: ```c snprintf(name, sizeof(name), "pbar_group.%d", pbp->pid); snprintf(name, sizeof(name), "pshell.%d", psh->pid); ```