add `#include <string>` to unicode.h (#5051)

Co-authored-by: Jared Van Bortel <jared@nomic.ai>

unicode.h

@@ -2,8 +2,9 @@
 
 #include <cassert>
 #include <stdexcept>
-#include <vector>
+#include <string>
 #include <unordered_map>
+#include <vector>
 
 static const std::vector<std::pair<uint32_t, uint32_t>> digit_ranges = {
 {0x30, 0x39}, {0xB2, 0xB3}, {0xB9, 0xB9}, {0x660, 0x669}, {0x6F0, 0x6F9}, {0x7C0, 0x7C9}, {0x966, 0x96F}, {0x9E6, 0x9EF}, {0xA66, 0xA6F}, {0xAE6, 0xAEF}, {0xB66, 0xB6F}, {0xBE6, 0xBEF}, {0xC66, 0xC6F},