Parser (src_bux/parser.bux):
- Increased struct field limit from 8 to 64
- Added field4-field7 slots in struct field assignment
- Safeguard: fields beyond slot 7 are parsed but not stored (counted only)
Known issues:
- buxc2 segfaults on ast.bux (Decl struct has 30+ fields, sizeof mismatch
between Bux parser's Decl and C compiler's Decl)
- Full bootstrap requires Decl struct in ast.bux to match actual Decl layout
All 18 examples pass, all unit tests pass.