feat: TVM String/File I/O Primitives

[gHashTag]

Implement 6 minimal opcodes for TVM runtime string and file I/O:

String I/O (3 opcodes)

• STR_LOAD (0x20): Load string literal from data section
• STR_CONCAT (0x21): Concatenate two string registers
• STR_PRINT (0x22): Print string to stdout

File I/O (3 opcodes)

• FILE_READ (0x23): Read file to string
• FILE_WRITE (0x24): Write string to file
• FILE_EXISTS (0x25): Check file exists

Implementation

• Modified: src/tri27/emu/decoder.zig
• Modified: src/tri27/emu/executor.zig

Status

✅ Opcodes added to decoder
✅ Execution handlers implemented
✅ Cycle estimates updated
✅ Tests passing

[gHashTag]

Implementation Complete

All 6 TVM String/File I/O primitives implemented:

String I/O (3 opcodes)

• STR_LOAD (0x20): Load string literal from .t27 data section
• STR_CONCAT (0x21): Concatenate two string registers
• STR_PRINT (0x22): Print string to stdout

File I/O (3 opcodes)

• FILE_READ (0x23): Read file to memory
• FILE_WRITE (0x24): Write string to file
• FILE_EXISTS (0x25): Check file exists

Files Modified

• src/tri27/emu/decoder.zig
• src/tri27/emu/executor.zig

Testing

• zig build test passes all existing tests
• No new memory allocations added

Commit: c90cb5d

Status: Ready for TVM integration tests