feat: add linear rope type

[k223kim]

Gemma3 uses the following config for rope:

    "rope_scaling": {
      "factor": 8.0,
      "rope_type": "linear"
    },

I added a linear rope type within extra_configs so that it can properly calculate theta.

Currently the HF transformer version does not have Gemma3, so it is skipped for pytest. With the newest version, it passes the test: see here.

[t-vi]

I wonder if this could be simplified but just handling a case where low_freq_factor/low_freq_factor is not given and having smooth_factor=0 in this case.

[ali-alshaar7]

LGTM!

[Borda]

@k223kim you may need this bump #1969 or make the import optional

[t-vi]

Seems good, thank you.

We could have a versioned skip to auto-enable, or point out the version that has gemma3, but let's have it as is now.

[t-vi]

Thank you @k223kim