update regex and parse to support multiple underscores in prefix

[sjakos]

Summary

This is an update of the parse and regex matches to support multiple underscores in the prefix for v0.3 of the spec.

[loreto]

@sjakos Thank you for putting together this PR (and apologies for the delay). Sending comments soon.

[loreto]

Technically this is not the right regex expression for two reasons:

1. It allows underscores at the beginning
2. It allows underscores at the end.

But underscores should only be allowed in the middle of the prefix. See https://github.com/jetify-com/typeid/tree/main/spec#type-prefix

The regex suggested there is ^([a-z]([a-z_]{0,61}[a-z])?)?$

[loreto]

In addition to changing the code, we should change the corresponding tests found here: https://github.com/jetify-com/opensource/blob/main/typeid/typeid-sql/supabase/tests/03_typeid.test.sql

To match the latest test cases from the spec:
https://github.com/jetify-com/opensource/blob/main/typeid/typeid/spec/valid.yml
https://github.com/jetify-com/opensource/blob/main/typeid/typeid/spec/invalid.yml

In particular the following test needs to be added to the valid ones:

# Tests below were added in v0.3.0 when we started allowing '_' within the
# type prefix.
- name: prefix-underscore
  typeid: "pre_fix_00000000000000000000000000"
  prefix: "pre_fix"
  uuid: "00000000-0000-0000-0000-000000000000"

This test needs to be removed from the invalid ones:

# Test removed in v0.3.0 – we now allow underscores in the prefix
# - name: prefix-underscore
#   typeid: "pre_fix_00000000000000000000000000"
#   description: "The prefix can't have symbols, it needs to be alphabetic"

And these two tests need to be added to the invalid ones:

# Tests below were added in v0.3.0 when we started allowing '_' within the
# type prefix.
- name: prefix-underscore-start
 typeid: "_prefix_00000000000000000000000000"
 description: "The prefix can't start with an underscore"

- name: prefix-underscore-end
 typeid: "prefix__00000000000000000000000000"
 description: "The prefix can't end with an underscore"

Let me know if you need some guidance adding and running the tests. Alternatively we can check in your code changes (once the regex is updated) and I can send a separate PR for the tests.