ww: lib tests run via -T test mode; bare mains retired (closes @test conversion)

'ww test' gains the istest build path (-T injection in build_one/
buildone) and do_test/dotest accept -I, mirroring do_run - both twins.
The 35 converted lib tests drop their interim bare mains (-T
synthesizes the entry from @test fns and rejects a user main); their
35 C run-drivers flip 'ww run' -> 'ww test'; 989_lib_byteid compiles
lib tests under -T (8 user-main probe fixtures stay non-T, gated on
the fixture field). Abort-on-first-failure stands until the deferred
record-and-continue harness lands with the multi-package arc.

lib/strconv/test/ftostest.ww

@@ -174,16 +174,3 @@ fn chkf32(n: f32, want: str) bool = {
 	assert(!(!rt64(math.f64frombits(0x0010000000000000u64))));	// F64_MIN_NORMAL
 	assert(!(!rt64(math.f64frombits(0x7FEFFFFFFFFFFFFFu64))));	// F64_MAX_NORMAL
 };
-
-export fn main() i32 = {
-	f64tos_fixed();
-	f64tos_scientific();
-	f64tos_special();
-	f32tos_fixed();
-	f32tos_scientific();
-	f32tos_extremes();
-	f32tos_special();
-	f64_roundtrip();
-	os.exit(0);
-	return 0;
-};