common-go v0.3.3 — the gorm logger stops leaking SQL

Traced statements were logged verbatim, so any literal inlined into a query --
an address in a WHERE, a token in an INSERT -- was copied into the log stream.
Statements are now redacted (quoted strings and numbers become ?), whitespace
collapsed, and the result truncated at 2048 bytes on a valid UTF-8 boundary.

Breaking for log consumers: the `sql` trace field is replaced by
`sql_preview` / `sql_bytes` / `sql_truncated`. Repoint any query on `sql`.

Adds errors.ErrUnavailable for a capability that exists but was never wired,
which ErrNotFound describes wrongly.