Fix high memory usage regression due to namespaces

[alx75]

This fixes the high memory usage regression that was introduced in 2.6.2. This fixes issue https://github.com/pythonicrubyist/creek/issues/122

Without this commit, when I try to parse a 33MB xlsx file (500_000 rows) and it consumes 8GB. With this commit it's consuming few hundreds (~300MB)

The reason lies in the namespaces due to all hash instantiation it does for all nodes.

Before this commit: Screencast from 2025-05-27 09-54-59.webm

With this commit: Screencast from 2025-05-27 09-58-59.webm