schemagen: support objects with more than 32 properties

Replace the 32-bit `uint32_t seen` bitmask with a `std::vector<uint64_t>`
bitset sized to the actual field count.  `requiredMask` is now a vector of
the same word count, and required-field checks use per-word masking so that
optional fields do not cause false rejections.

Adds big.schema.json + test_big.cpp regression tests covering the issue
reproducer (40 required properties, missing/duplicate at index 32), plus
run_tests.sh to exercise both test_gen.cpp and test_big.cpp.

Fixes #3

contrib/schemagen/run_tests.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+# Build and run the schemagen regression tests.
+# Expects weaseljson to be built at ../../build (the default CMake build dir).
+set -euo pipefail
+
+cd "$(dirname "$0")"
+
+python3 weaseljson_schemagen.py example.schema.json -o gen.h --namespace weasel_schema
+python3 weaseljson_schemagen.py big.schema.json -o big.h --namespace big_schema
+
+g++ -std=c++20 -I../../include -I. test_gen.cpp \
+    -L../../build -lweaseljson \
+    -Wl,-rpath,'$ORIGIN'/../../build \
+    -o test_gen
+
+g++ -std=c++20 -I../../include -I. test_big.cpp \
+    -L../../build -lweaseljson \
+    -Wl,-rpath,'$ORIGIN'/../../build \
+    -o test_big
+
+./test_gen
+./test_big