Inline single-use env wrappers

[python-processing-unit]

Problem

The following env.h functions each have exactly 1 caller and are thin wrappers around ns_buffer or _direct variants: env_retain, env_exists, env_freeze, env_thaw, env_permafreeze, env_frozen_state, env_permafrozen.

Fix

Inline each at its single call site, or collapse into the underlying ns_buffer/_direct call.

Reported by Kilo Code (automated audit tool), not a human reviewer.