feat: support sha2 and sha2_hex with digest size of 256

[ifm-pgarner]

We're using Snowflake sha2 function in our project that uses fakesnow for testing (it's great, thank you!)

But duckdb does not have sha2 function, instead it has a sha256 function

sha256(foo) is the same as Snowflake sha2('foo', 256) (or you can omit the length arg and it defaults to 256) https://docs.snowflake.com/en/sql-reference/functions/sha2#arguments

So this PR adds a transform for these function calls

[tekumara]

looks great, thank you for this!

[tekumara]

would you mind also adding a test to test_fakes.py too? this will guarantee integrated test coverage that includes duckdb's execution

[ifm-pgarner]

added now, thanks

[anentropic]

I realised I could use sha2_binary and store my hashes in a 32 byte column instead of varchar(64) for hexdigest

duckdb doesn't have that function but unhex(sha256(...)) seems to give same result

In [24]: duckdb.sql("SELECT unhex(sha256('Snowflake'))").show()
┌────────────────────────────────────────────────────────────────────────────────────────┐
│                               unhex(sha256('Snowflake'))                               │
│                                          blob                                          │
├────────────────────────────────────────────────────────────────────────────────────────┤
│ \x1D\xBDY\xF6a\xD6\x8B\x90rO!\x08C\x96\xB8eIqs\xE4\xD2qOM\x91\xCF\x05\xFA_\xC5\xE1\x8D │
└────────────────────────────────────────────────────────────────────────────────────────┘


In [25]: sha256(b"Snowflake").digest()
Out[25]: b'\x1d\xbdY\xf6a\xd6\x8b\x90rO!\x08C\x96\xb8eIqs\xe4\xd2qOM\x91\xcf\x05\xfa_\xc5\xe1\x8d'

so I have added that transform as well

[tekumara]

Perfect, thank you!