More possible macros to add

for cross db compatibility and making packages easier to use:
* `ceiling` - `ceiling` in spark but `ceil` in snowflake
* `list_agg`/`string_agg` is `concat_ws({{ delimiter }}, collect_list({{ field_to_agg }})`

Start by locating the existing macro definitions and tests for cross-database functions, then inspect how this package exposes Spark utility macros. Done means adding the requested ceiling and list/string aggregation macros with the stated function mappings and coverage for their expected inputs.

Written by the indexing model from the issue text.