trailingMetadataStringAssumeCapacity

pub fn trailingMetadataStringAssumeCapacity(self: *Builder) Metadata.String {
    const start = self.metadata_string_indices.last().?;
    const bytes: []const u8 = self.metadata_string_bytes.items[start..];
    assert(bytes.len > 0);
    const gop = self.metadata_string_map.getOrPutAssumeCapacityAdapted(bytes, Metadata.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 @fromBackingInt(@intCast(gop.index));
}