* Make encode and encode_by_ref fallible
This only changes the trait for now and makes it compile, calling .expect() on all users. Those will be removed in a later commit.
* PgNumeric: Turn TryFrom Decimal to an infallible From
* Turn panics in Encode implementations into errors
* Add Encode error analogous to the Decode error
* Propagate decode errors through Arguments::add
This pushes the panics one level further to mostly bind calls. Those will also be removed later.
* Only check argument encoding at the end
* Use Result in Query internally
* Implement query_with functions in terms of _with_result
* Surface encode errors when executing a query.
* Remove remaining panics in AnyConnectionBackend implementations
* PostgreSQL BigDecimal: Return encode error immediately
* Arguments: Add len method to report how many arguments were added
* Query::bind: Report which argument failed to encode
* IsNull: Add is_null method
* MySqlArguments: Replace manual bitmap code with NullBitMap helper type
* Roll back buffer in MySqlArguments if encoding fails
* Roll back buffer in SqliteArguments if encoding fails
* Roll back PgArgumentBuffer if encoding fails
