Vector types (SIMD): f32x8, i8x32, f64x4 and the rest; --cpu native

- fNxM / iNxM / uNxM up to 512 bits, as LLVM vectors (<8 x float>): LLVM picks SSE, AVX2,
  AVX-512 or NEON for them
- f32x8(x) in every lane, f32x8(a, ..., h), f32x8(list, i) loads, f32x8(i32x8 v) converts
- + - * / and the bit operators lane by lane, with a plain number on either side counting for every lane;
  v[i], v[i] = x, v.len, == / != (every lane), print and str
- methods: sum min max dot abs sqrt floor ceil round fma store; min/max/abs/clamp lane by lane
- wide vectors (and structs holding them) are loaded and stored with align 16, what malloc and the stack give
- --cpu <name> (and cpu = "..." in finch.toml): native, x86-64-v3, apple-m1, ...
- debug info shows vectors; the language server completes their methods; Kate and VS Code highlight them
- f32 x = -1.5 works: a minus in front of a float written in the code keeps it such a number

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Psc42moPLwP43Cmb9oZqSR

tests/fail/vec_mix.fch

@@ -0,0 +1,6 @@
+// expect: can't use '+' on f32x8 and i32x8 (convert one: f32x8(...))
+fn main() {
+    a := f32x8(1.0)
+    b := i32x8(1)
+    print(a + b)
+}