trailingMetadataStringAssumeCapacity

pub fn trailingMetadataStringAssumeCapacity(self: *Builder) MetadataString {
    const start = self.metadata_string_indices.getLast();
    const bytes: []const u8 = self.metadata_string_bytes.items[start..];
    const gop = self.metadata_string_map.getOrPutAssumeCapacityAdapted(bytes, String.Adapter{ .builder = self });
    if (gop.found_existing) {
        self.metadata_string_bytes.shrinkRetainingCapacity(start);
    } else {
        self.metadata_string_indices.appendAssumeCapacity(@intCast(self.metadata_string_bytes.items.len));
    }
    return @enumFromInt(gop.index);
}