[Pg] Fix introspecting `varchar[]` doesn't parse length correctly

[akshitkrnagpal]

Fixes #1633

The change finds length of the varchar by finding ( and ) characters, instead of fixed values. It also handles the case when no length is provided.

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I have also considered removing [] from the lowered variable and that would work with other types also. Here is the commit for that - https://github.com/drizzle-team/drizzle-orm/commit/79b0609fe801c467f30292a815cd1c039f341df5

Lmk which one you prefer.