[Code scan] Forward c in make_graphene_rect's reshape path

This issue comes from a Codex global scan of deepmodeling/tbplas at commit 4d3652b3dba8eb930e4869a6d41074f62d703692.

Severity: Medium

`make_graphene_rect(from_scratch=False, c=...)` rebuilds the rectangular cell by reshaping a diamond graphene cell, but it calls `make_graphene_diamond(t=t)` without forwarding `c`. Callers who request a non-default c-axis get a reshaped cell based on `c=1.0` instead.

Code reference:
https://github.com/deepmodeling/tbplas/blob/4d3652b3dba8eb930e4869a6d41074f62d703692/tbplas/materials/graphene.py#L68-L71

Suggested fix: call `make_graphene_diamond(c=c, t=t)` in the reshape branch.

Read tbplas/materials/graphene.py around lines 68-71 and trace the reshape branch of make_graphene_rect. Verify that a non-default c value is passed through to the diamond-cell construction and that the resulting rectangular cell uses that value.

Written by the indexing model from the issue text.