Use random identifier in DuckDB attachment name

[phillipleblanc]

This PR addresses a concurrency issue where multiple queries attempting to attach the same DuckDB database would fail with catalog write-write conflicts.

Problem

When multiple queries run concurrently and each tries to attach a database using the same attachment name (e.g., "attachment_0"), they create separate transactions that attempt to modify DuckDB's catalog simultaneously. DuckDB enforces strict serialization of catalog modifications to maintain consistency, causing errors like:
TransactionContext Error: Catalog write-write conflict on create with "attachment_0"

Example of the failing scenario:

Query 1: BEGIN
Query 1: Check if attachment_0 exists (sees it doesn't exist)
Query 2: BEGIN
Query 2: Check if attachment_0 exists (sees it doesn't exist)
Query 1: Try to create attachment_0
Query 2: Try to create attachment_0 -> CONFLICT! Transaction 1's change is not visible in Transaction 2's snapshot

Solution

Instead of having concurrent transactions compete to create the same attachment name, we now generate a unique identifier for each attachment. This means each transaction creates its own uniquely named attachment, avoiding catalog conflicts entirely.