Extract module for overriding `find` with Slugify

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You can find record with Avram's built-in query methods.

```crystal
ArticleQuery.new.slug("avram-is-a-great-orm").first
```

Or if you want to add a shortcut you can do something like this:

```crystal
class ArticleQuery < Article::BaseQuery
def find(slug_or_id : String | Int64) : Article
if slug_or_id.is_a?(Int64)
previous_def(slug_or_id)
else
slug(slug_or_id).first
end
end
end

# Find by slug
ArticleQuery.find("avram-is-a-great-orm")
# Find by id
ArticleQuery.find(1_i64)
# Can be scoped like any other query
ArticleQuery.new.account_id(account.id).find("avram-is-a-great-orm")
```

So you can just `include AvramSlugify::Finder` in your Query class

Start with Avram's query methods and the ArticleQuery example in the issue, then inspect how Query classes expose find and slug. Extract the shown behavior behind AvramSlugify::Finder and verify that including it supports both slug and Int64 lookups, including scoped queries.

Written by the indexing model from the issue text.