feat(experimental): shuffle packages & add explicit provider Go func registration

[mfridman]

Note

All changes are in ./interal. No changes to the core goose package.

The main goal of this PR is to add the ability to register Go migration functions explicitly on the goose.Provider, instead of solely using func init() { goose.AddMigration(..., ...) }. (note, both explicit and init Go migrations are merged together by version).

This is very useful for creating a closure over Go migration functions for DI purposes.

In the process, a few things were refactored and a bunch more tests were added. Of note,

• Collapse package migrate and package provider into one
• Remove redundant Go/SQL types
• Add new type GoMigration to be used with WithGoMigration
• Add ParseAllFromFS to package sqlparser with tests

// GoMigration is a user-defined Go migration, registered using the option [WithGoMigration].
type GoMigration struct {
	// One of the following must be set:
	Run func(context.Context, *sql.Tx) error
	// -- OR --
	RunNoTx func(context.Context, *sql.DB) error
}

// WithGoMigration registers a Go migration with the given version.
//
// If WithGoMigration is called multiple times with the same version, an error is returned. Both up
// and down functions may be nil. But if set, exactly one of Run or RunNoTx functions must be set.
func WithGoMigration(version int64, up, down *GoMigration) ProviderOption {
	...
}