fix(deberta-v2): move "Copied from" comments above @torch.jit.script for Python 3.13 compat

[s-zx]

Summary

Importing DebertaV2Model (or anything that depends on it, e.g. gliner) raises
IndentationError on Python 3.13 because torch.jit.script calls inspect.getsource(),
dedents the snippet, and passes it to ast.parse(). Python 3.13's stricter parser rejects
a comment placed between a decorator and the def statement.

Root Cause

Three functions in modeling_deberta_v2.py had a # Copied from ... comment between
@torch.jit.script and def:

@torch.jit.script
# Copied from transformers.models.deberta.modeling_deberta.c2p_dynamic_expand
def c2p_dynamic_expand(...):
    ...

Fix

Move each # Copied from comment to the line above its @torch.jit.script decorator:

+# Copied from transformers.models.deberta.modeling_deberta.c2p_dynamic_expand
 @torch.jit.script
-# Copied from transformers.models.deberta.modeling_deberta.c2p_dynamic_expand
 def c2p_dynamic_expand(...):

Applied to all three affected functions (c2p_dynamic_expand, p2c_dynamic_expand,
pos_dynamic_expand).

Fixes #44855

[github-actions]

[For maintainers] Suggested jobs to run (before merge)

run-slow: deberta_v2, gpt_neox