Struct defaults apply inside structs; exit() ends an or-block; 1e9 literals; x * 2.0 stays f32; floats print as the shortest exact text; str(x, digits)

Also frees main's args and the message of a failing main (valgrind was not clean on two tests).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/new/defaults_numbers.fch

@@ -0,0 +1,43 @@
+// struct defaults apply inside structs too; number literals and float text
+
+struct Audio {
+    int rate = 48000
+    float volume = 0.8
+}
+
+struct Mixer {
+    Audio audio
+    []Audio extra
+    int voices = 5
+}
+
+struct Box[T] {
+    T item
+    Audio audio
+}
+
+fn make() -> Mixer {
+    Mixer m
+    return m
+}
+
+fn scale(f32 x) -> f32 {
+    return x * 2.0 + 1
+}
+
+fn main() {
+    a := Mixer()
+    Mixer b
+    c := Mixer(voices: 2)
+    list := [Mixer()]
+    m := ["x": Mixer()]
+    map[str]Mixer counts
+    counts["new"].voices += 1
+    bx := Box[int]()
+    print(a.audio.rate, b.audio.volume, c.audio.rate, c.voices, list[0].audio.rate, m["x"].audio.rate)
+    print(make().audio.rate, counts["new"].audio.rate, counts["new"].voices, bx.audio.rate)
+
+    print(1e3, 2.5e-3, 1E+6, 1_000.5e1, scale(1.5))
+    print(1.0 / 3.0, 0.1 + 0.2, 100000000.0, 1e20, 1e-7, float(7), f32(0.1))
+    print(str(3.14159, 2), str(2, 1), str(f32(0.1)), "x=" + str(0.25), [0.5, 1.25])
+}