Handle T_1 in supersingular Hecke matrices

[OutisNemosseus]

Description

The generic Hecke framework treats T_1 as the identity, but
SupersingularModule.hecke_matrix() overrides the generic implementation
and does not handle L = 1.

As a result,

SupersingularModule.hecke_matrix(1)
-> Phi_polys(1, ...)
-> pari.polmodular(1)
-> PariError: domain error in polmodular_ZM: L < 2

This adds the missing L == 1 identity case and a regression doctest.

Testing

The modified ssmod.py was loaded directly from this branch and checked with:

T1 =
[1 0 0]
[0 1 0]
[0 0 1]

T1 identity: PASS
T2 control: PASS

git diff --check and git show --check pass.

[OutisNemosseus]

T1bugReproduction.ipynb
supersingular_T1_bug_evidence_chain_v5_runtime_trace (3).ipynb

[OutisNemosseus]

https://hub.bids.mybinder.org/user/outisnemosseus-sage-t1-binder-o1iv8wh8/lab/workspaces/auto-r/tree/T1bugEvidenceChain.ipynb
https://hub.bids.mybinder.org/user/outisnemosseus-sage-t1-binder-o1iv8wh8/lab/workspaces/auto-r/tree/T1bugReproduction.ipynb

[github-actions]

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