Fix: Add missing init file to sqlfluff.core.templaters.slicers

[CrossNox]

Brief summary of the change made

Running sqlfluff --help (or any CLI command) fails with ModuleNotFoundError: No module named 'sqlfluff.core.templaters.slicers' due to a missing __init__.py file on src/sqlfluff/core/templaters/slicers.

Are there any other side effects of this change that we should be aware of?

None

[CrossNox]

I just noticed that 1788 adds this file, but IMHO this quick fix can be isolated into a small PR and then merge those changes, so that main has a runnable version.

[codecov]

Codecov Report

Merging #1826 (560dbc2) into main (8719730) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main     #1826   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          138       138           
  Lines         9832      9832           
=========================================
  Hits          9832      9832           

Impacted Files	Coverage Δ
src/sqlfluff/core/templaters/jinja.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8719730...560dbc2. Read the comment docs.

[tunetheweb]

Can you add the comment like #1788 does to prevent linting failures.

@barrywhart you happy for this to go ahead of your PR?

[barrywhart]

Sure, go ahead. Not sure when mine will be finished.

[CrossNox]

Can you add the comment like #1788 does to prevent linting failures.

@barrywhart you happy for this to go ahead of your PR?

Added! @barrywhart I couldn't find a way to checkout the file from your fork so that it appeared as authored by you, sorry.

[barrywhart]

No worries!

[WittierDinosaur]

Perhaps it's worth adding a test case for this?

[CrossNox]

@WittierDinosaur do you mean testing the CLI or testing imports?

[tunetheweb]

Presume he means to prevent this issue happening again in the future where a new module is added without a __init__.py when it's needed?

Would be good if we could add that. But think out of scope of this PR so let's merge this.