Change ISqlAdapter Insert contract to return a long instead of int

[ghost]

Fix for #1385

[NickCraver]

Hey there! Unfortunately, this is a breaking change we can't make - it's something we're likely to change the workings on in v3 (see #722), but changing the interface here would break all consumers so it's not a change we can take to the lib until a major version...which will get a refactor when time allows anyhow.

[NickCraver]

I can't speak to Contrib's future plans here and if this is a good fit, but please see #1658 - Dapper.Contrib is not located at https://github.com/DapperLib/Dapper.Contrib (separate from this repository).

Note: I based the Dapper.Contrib fork on the original codebase which hopefully makes porting pull requests against the main branch there much easier - the intent was to split, not throw away work the community wants to go with.