engine: regexp_substr

[DanCodedThis]

Closes #134

• regexp_substr impl
• Uses an iterator approach for performance and reusability
• Docs
• Extensible insta tests
• SLT tests

P.S. Small position argument error change in regexp_instr

Reference: https://docs.snowflake.com/en/sql-reference/functions/regexp_substr

[github-actions]

✅ SLT Targeted Testing: No relevant SLT tests found for the changes in this PR. No testing required.

[DanCodedThis]

✅ SLT Targeted Testing: No relevant SLT tests found for the changes in this PR. No testing required.

@andheroe Second time tests are not selecting again.

[DanCodedThis]

✅ SLT Targeted Testing: No relevant SLT tests found for the changes in this PR. No testing required.

@andheroe Second time tests are not selecting again.

Will check it out locally.

[github-actions]

✅ SLT Targeted Testing: No relevant SLT tests found for the changes in this PR. No testing required.

[DanCodedThis]

I validated, the regexp_substr. Again surprised, even the ip apache service info regex in the json_object cases worked like a charm.