feat: Customizable column types and validators

[melgenek]

Signed-off-by: Yevhenii Melnyk melnyk.yevhenii@gmail.com

Partially closes #36.

Rationale for the change

I'd like to introduce column type verification for Datafusion apache/datafusion#4499.

In order to let downstream users of sqllogictest-rs to define custom column types and validation strategies, I suggest introducing a pluggable column type. This way different AsynDB and DB implementations would be able to define column types beyond the original 'T','I','R' like CocroachDB does, or shrinking the set of columns to only having I like DuckDB suggests.

Changes

This pr introduces an interface ColumnType and a default implementation DefaultColumnType that is similar to the original Sqllites type, except that it accepts any letters and parses them as an "Any" type.

Another change is a customizable validator for columns in results. By default, the behaviour is the same as before: neither the number nor type of the columns is validated.

Changes visible to the client

• AsyncDB and DB implementations would need to explicitly define an associated type ColumnType.
• The run method would need to change the definition

from 
fn run(&mut self, sql: &str) -> Result<DBOutput> {...}

to 
fn run(&mut self, sql: &str) -> Result<DBOutput<Self::ColumnType>, FakeDBError> {...}

• ColumnType::Any -> DefaultColumnType::Any
• The way to call update_test_file would change from update_test_file(.., runner, ..) to runner.update_test_file(...)

[xxchan]

Thank you very much for your recent contributions! I'm sorry that I havn't have a change to look at them. I will take a look soon. Also cc @skyzh do you have time to take a look? 🫣

[skyzh]

LGTM! Thanks a lot for this great work!

Given this is a breaking change, we will need to release a minor version for the current main branch before merging this PR. I will do it today.

[melgenek]

@skyzh Wow, thank you for so fast review!