[BUG] DistributedOptimizer issues in Mixed-Precision: Stale model_param_group_index_map and .copy_ failure during get/load parameter_state

**Describe the bug**

During mixed-precision training (BF16 & FP32, FP8 is optional), a RuntimeError (size mismatch) is triggered when saving a checkpoint via `get_parameter_state_dp_zero`.

Based on our analysis, the hardcoded parameter reordering in `_build_model_and_main_param_groups` within `DistributedOptimizer` causes the `self.model_param_group_index_map` to become out of sync with the actual `optimizer.param_groups`.

**Steps/Code to reproduce bug**

1. Before building the DDP model and optimizer，use `Float16Module` to wrap the model for BF16 training, but manually promote certain modules (both params and inputs) to FP32.
2. Train for several steps.
3. Call `get_parameter_state_dp_zero` in `DistributedOptimizer` to collect optimizer states, which triggers the size mismatch error.

**Root Cause Analysis**

1. Initial Map Construction: In `__init__`, `self.model_param_group_index_map` is first constructed via `_build_optimizer_group_ranges`. This map records the position `(group_index, group_order)` of param in param_groups

2. Hardcoded Reordering: Subsequently, `_build_model_and_main_param_groups` reorders the parameters within each group (placing native FP32 shards at the front and main parameter shards converted from FP16/BF16 at the back) and updates `optimizer.param_groups` accordingly:

3. Index Invalidation: The `model_param_group_index_map` is not updated after this reordering. Consequently, downstream functions like `_get_main_param_and_optimizer_states` retrieve the wrong Tensors using stale group_order indices, leading to shape mismatches during buffer copy operations.

**Additional question**

1. What is the design motivation behind this specific reordering (grouping by DType)?
2. What is the recommended best practice to fix this: disabling the reordering to maintain discovery order consistency, or explicitly updating the `model_param_group_index_map` after the reordering is performed?