memcopy! and memset! intrinsics

TODO.md

@@ -934,6 +934,20 @@
   - fields without defaults remain required; C-layout records, unions, tuples, and anonymous
     generated structs do not accept defaults
 
+45. typed memory intrinsics (implemented)
+  - `memcopy!` copies equal-length, non-overlapping slices or pointers-to-arrays with identical
+    element types; comptime diagnoses invalid regions and runtime guards length, size, and overlap
+  - `memset!` fills a mutable region with a value coerced to its element type; bytes lower to LLVM
+    memset and wider values use typed stores
+  - both operations evaluate operands once, preserve undefined state without observing it, and work
+    identically during comptime evaluation; zeroing is `memset!(destination, 0)`
+  - `std/mem` aligned reallocation uses `memcopy!`
+
+46. fix `EnumFieldStruct` in `std/meta`
+  - currently, the `|info|` `.enum` payload capture doesn't preserve the comptime-ness in the match statement
+    this results in having to type other values in the scope like `[field!(typeinfo!(E), "enum").fields.len]mut []u8`
+    which is obviously absurd
+
 ## A word on unchecked casts
 
 For casts that bypass safety checks, Honey provides builtin functions: