Removes `__block_invoke_void` / `__block_invoke_bool` and their
companion `Into(Block)` impls from
`library/modules/std/objc_block.sx`. The generic
`Into(Block) for Closure(..$args) -> $R` impl from step 5.2 now
covers both shapes (and every other closure shape) via per-mono
`#insert build_block_convert($args, $R)` source emission.
Net stdlib shrinkage: ~52 lines, two trampolines + two per-shape
impls down to zero. Adding a new block-shape consumer no longer
requires touching stdlib — the impl emits per-call-shape on
demand.
`examples/95-objc-block-noop.sx` (zero-arg closure) and
`examples/96-objc-block-multi-arg.sx` (user-declared per-shape
impl for `Closure(s32, *void) -> void`) still pass: 95 routes
through the new generic, 96 keeps its in-file impl as a
documentation example of the user-declares-their-own path.
Suite at 217/217.
2eaf932fcf