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fix(transpiler): keep Evolution synthesis and atomicity in qDRIFT (#330)

The sampled gates were built without either keyword-only attribute of the
gate they replace, which cost two distinct things.

A caller's `synthesis` method was silently replaced by the default
`FermionicLieTrotter`. This was observable whenever the Hamiltonian carried
groups, since a sampled group holds more than one term and so does not hit
the single-factor short circuit.

Not marking the gates atomic mattered more. A sampled group is a terminal
factor, but it was still decomposable, and `split_out_groups` drops the
grouping, so decomposing re-split it term by term. An individual term is
generally not Hermitian even when its group is (the conjugate pairs of a
`UCC` cluster generator being the motivating example), so those factors are
not unitary and the fermion-to-qubit stage rejected them with a `ValueError`
about complex coefficients. This is the same defect that introducing
`Evolution.atomic` fixed for the factors emitted by a synthesis method;
qDRIFT was the one remaining producer that never got it.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

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