refactor: use cfg predicates in macroweave rows

[tisonkun]

Summary

• Consolidate pointer-width-specific macroweave expansions by treating cfg predicates as a repeat column.
• Use all() for unconditional rows and target_pointer_width predicates for usize rows.
• Remove duplicated stable and nightly expansion bodies while preserving behavior.
• Verify the change with cargo x test and cargo x lint.