disables ZeRO checkpoint loading path when stage=0 (#7586)
Fixes #7571
When ZeRO is disabled (stage 0) and bf16 is enabled, the current guard
sets `load_zero_checkpoint=True`, which leads to `_load_zero_checkpoint`
and `_restore_from_bit16_weights()` being called even though no ZeRO
state exists.
This PR removes the `self.bfloat16_enabled()` condition so that
load_zero_checkpoint is tied strictly to `self.zero_optimization()`.
Stage 0 (BF16/FP16/FP32): cleanly skips ZeRO checkpoint path.
Stage ≥ 1: loads ZeRO partitioned optimizer state as before.
cc @sfc-gh-truwase
Signed-off-by: Naveenraj Kamalakannan <therealnaveenkamal@gmail.com>
Co-authored-by: Olatunji Ruwase <tunji.ruwase@snowflake.com>
