Logs the four commits that closed out step 1 of the variadic
heterogeneous type packs feature:
- 1c.A: parser-rejection lock-in for `..$args` inside `Closure(...)`.
- 1c.B: parser + AST + types.zig `pack_start` representation.
- 1d.A: impl-matching concrete-only miss lock-in.
- 1d.B: pack-aware impl matching with $args + $R binding through
`param_impl_pack_map` and `pack_bindings`.
Next step is plan step 2 — runtime `args[$i]` indexing + per-mono
mangling — opening the door to body-side pack reflection that
step 5 needs to retire the hand-rolled `Into(Block)` impls.
Also catches up the 1b entry which the prior session left
uncommitted in the working tree.
35ef32ffdb