finch.toml, threads and atomics, finch fmt, C++ files, struct #defines, a struct variable given for its ptr

- finch.toml: name, entry, paths, include, links, libdirs, cflags, ldflags, and [target.windows] etc.;
  finch run / build / test with no file use its entry
- import thread: spawn, join, mutex, cpus; atomic_add/sub/load/store/swap/cas built in
- finch fmt [--check]: indentation by { }, trailing spaces, empty lines; also as LSP formatting
- link "x.cpp" (or in finch.toml): built with the C++ compiler, which then links (FINCH_CXX)
- #define RAYWHITE (Color){ 245, 245, 245, 255 } imports as a Color
- push(body) where push takes ptr[Body]: the same as push(addr(body))
- --target android (NDK clang from ANDROID_NDK_HOME, -llog)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016GzNP6r8dg6WDxUVZy8wjL

tests/new/interpolation.fch

@@ -0,0 +1,21 @@
+// "\(x)" in text
+struct P {
+    int x
+    float y
+}
+
+fn main() {
+    name := "Ada"
+    hp := 7
+    p := P(x: 3, y: 0.25)
+    print("hi \(name), hp \(hp), next \(hp + 1)")
+    print("p = (\(p.x), \(p.y, 2)) \("nested \(name)")")
+    map[str]int m
+    m["k"] = 5
+    print("\(m["k"]) \(str(1.0 / 3.0, 3))")
+    print("no code here: \\(x) and \t tab")
+    long := """
+        speed \(p.y * 4.0)
+        """
+    print(long)
+}