nx_addr2line.nx

nx_addr2line.nx -- sovereign addr2line. Given an ELF + a code address, walk the DWARF .debug_line program and return the source (file_idx, line) at that address. Foundation for the future nx_dbg.nx debugger ("show me the source line at PC") + sovereign nx_panic backtraces with file:line locations. What we do (DWARF v5 §6.2 line-program VM): 1. Locate .debug_line section via nx_elf_read. 2. Decode the line-program header (file table + dir table). 3. Run the line-program VM until address >= target_addr or end. 4. Return the (file_idx, line) of the most recent committed row whose address <= target. Pairs with nx_dwarf_line.nx which BUILDS the section; together, produce + consume the same byte format with our own code only. v0.0.1 scope: * Decode the standard opcodes our nx_dwarf_line emits: DW_LNS_copy, DW_LNS_advance_pc, DW_LNS_advance_line, DW_LNS_set_file * Decode extended ops: DW_LNE_end_sequence, DW_LNE_set_address Special opcodes (the compact bias-encoded form) NOT yet decoded; our emitter doesn't use them today. Add when the emitter does.