fix: add namespace to adapter.dispatch(), qualify macro calls

[pinkberg-eh]

Before this PR, I was getting compiler errors from dbt_synth_data like:

Compilation Error in model _my_model_fixture (models/.../fixtures/_my_model_fixture.sql)
  In dispatch: No macro named 'synth_distribution_continuous_uniform' found within namespace: 'None'
      Searched for: 'snowflake__synth_distribution_continuous_uniform', 'default__synth_distribution_continuous_uniform'
  
  > in macro synth_distribution_continuous_uniform (macros/distributions/continuous/uniform.sql)
  > called by macro synth_distribution_discrete_probabilities (macros/distributions/discrete/probabilities.sql)
  > called by macro synth_distribution_discrete (macros/distributions/util.sql)
  > called by macro synth_distribution (macros/distributions/util.sql)
  > called by model _my_model_fixture (models/.../fixtures/_my_model_fixture.sql)

I'm compiling against Snowflake, but I believe this affects all adapters.

This regression may have been caused by DBT's choice to move adapters out of dbt-core.

[tomreitz]

Thanks so much for the contribution, @pinkberg-eh!

We've been getting around this by setting

macro-paths: ["macros", "dbt_packages/dbt_synth_data/macros"]

in dbt_project.yml, but that's a workaround, not a solution. Yours is the correct approach here; I've tested and approve.