LeoDog896 has created PR #500: test(fuzz): read -> write bson in bson-rust

Issue Text:
Runs `to_writer` in fuzz tests. Makes the fuzzer slower, but covers any write errors. Also adds a fuzz test for `from_slice_utf8_lossy`.

Note: I did not check for equivalence in `from_reader` and `to_writer`, as, even for accounting for length, there is still some loss in data from the reader, as to be expected.