Merge branch 'ps/reftable-strbuf' into ps/reftable-detach

* ps/reftable-strbuf: reftable: handle trivial `reftable_buf` errors reftable/stack: adapt `stack_filename()` to handle allocation failures reftable/record: adapt `reftable_record_key()` to handle allocation failures reftable/stack: adapt `format_name()` to handle allocation failures t/unit-tests: check for `reftable_buf` allocation errors reftable/blocksource: adapt interface name reftable: convert from `strbuf` to `reftable_buf` reftable/basics: provide new `reftable_buf` interface reftable: stop using `strbuf_addf()` reftable: stop using `strbuf_addbuf()`