Align the non-idle GeneralNoiseModel surfaces (gate/emission/leakage/measurement/crosstalk) with the structured noise vocabulary #425

Goal

Survey and align the non-idle surfaces of GeneralNoiseModel with the structured
noise-vocabulary conventions established for idle noise (one rate + one relative-rate
model per channel family, law in the name, symmetric defaults where physical, first-class
alphabet keys, fail-loud on ambiguity), so the whole model reads as one system.

Idle noise is covered separately by #424 (deprecation ramp). This issue is the remainder:

• Gate noise: p1 + p1_pauli_model, p2 + its two-qubit weighted sampler
  (crates/pecos-engines/src/noise/weighted_sampler.rs — X/Y/Z/L and pair-string
  alphabets). Already close to the rate+model shape; audit naming, defaults, and
  validation tolerances against the structured conventions.
• Emission: p1_emission_ratio / p2_emission_ratio and emission models — ratios vs
  rates vs models; decide the consistent spelling.
• Leakage: leakage_scale (0.0 = replace leakage with depolarizing, 1.0 = keep) —
  interacts with every model containing L; needs an explicit place in the vocabulary.
• Measurement/prep: asymmetric bit-flip and prep-leak parameters.
• Crosstalk models: CrosstalkWeightedSampler alphabet and its DEM-side counterpart
  (p_meas_crosstalk_* in the DEM builder) — same-vocabulary check across consumers.
• Builder input rescaling: the same unit trap documented in Deprecation ramp: align pecos-engines GeneralNoiseModel idle-noise API with the structured vocabulary #424 applies wherever the
  fluent builder rescales inputs; any renamed parameter needs the numerically equivalent
  spelling in its warning.

Constraint

Same as #424: external users — staged additive/warning/removal ramp, never a hard rename.

Related: #420 (layer-1 idle families), #422 (native-surface NoiseModel port), #423
(layer-2 idle-channel vocabulary), #424 (idle-noise ramp for this model).