Remove driver related bloat from go.mod

[slsyy]

Right now the go.mod contains a lot of dependencies from specific driver libraries. However they are not used at all in the core library, because each implementation use the standard database/sql interface.

Problems with that approach:

• huge number of dependencies looks just scary. People prefer libraries with a minimal set of dependencies
• dependency clash, which make upgrades more challenging. Right now I have this problem in my private project, because go.opentelemetry.io/otel is quite popular and it notoriously break the backward compatibility
• it will be worse and worse with the addition of new drivers. For example the recent CloudSpanner PR https://github.com/go-testfixtures/testfixtures/pull/211/files#diff-33ef32bf6c23acb95f5902d7097b7a1d5128ca061167ec0716715b0b9eeaa5f6

Maybe it would be helpful to extract all of the test to separe go.mod within the repo, so the core library is super lean. @andreynering WDYT?

[andreynering]

Hey @slsyy,

I always wanted to solve this problem, but never knew how exactly, and didn't have a lot of time to try.

On other package panagers (Bundler for Ruby, etc) you specify a dependency as being dev or test, so it is ignored on importers, but Go do not have such concept.

If you think having a separate go.mod would work, I'm more than happy to review a pull request for it.

[wxiaoguang]

also: Split database supports into separate packages? #241

[ccoVeille]

Maybe it would be helpful to extract all of the test to separe go.mod within the repo, so the core library is super lean

I also think it's a good approach.

[ccoVeille]

I also suggested something here

#241 (comment)

Please tell me if you think it could help