Fix Gemma2/3 GGUF rename rules + drop GGUF runtime-aux tensors
Gemma-2 and Gemma-3 have four layer norms per block (input,
post-attention, pre-feedforward, post-feedforward) but the converters
shared `_NEMOTRON_CONVERTERS` which only handled two of them, and
incorrectly mapped `ffn_norm` to `post_attention_layernorm`. Gemma-3
additionally has per-head q/k RMSNorm. Result: silent re-init of
`pre_feedforward_layernorm`, `post_feedforward_layernorm`,
`self_attn.{q,k}_norm` from defaults.
Split into `_GEMMA2_CONVERTERS` and `_GEMMA3_CONVERTERS` with the
correct four-norm mapping (plus q/k_norm for Gemma-3), all wrapped
in `SubtractOne` since Gemma stores RMSNorm weights as `w + 1`.
Also drop `rope_freqs.weight` at GGUF load: GGUF ships it as runtime
metadata, but HF models compute RoPE frequencies from config — so it
showed up as an "unexpected" key on Llama-3 etc.
Add `tests/quantization/ggml/test_gguf_load_completeness.py` — slow
test that loads one representative GGUF per registered model_type and
asserts zero missing / unexpected / mismatched keys, so future rename
regressions fail fast instead of silently re-initing parameters.