Add Thermic source in core layer

[pluAtAnsys]

📝 Description of the feature

Add thermic source in core layer inside the core.source module
follow the same architecture based on the exisiting source example
set the default value as those in SCDM Speos.
create documentation example inside the core section
create unit test for thermic source in core section

Make sure the code coverage is higher 85%
Update the .toml file to use ansys_api_speos to 0.15.0

💡 Steps for implementing the feature

No response

🔗 Useful links and references

Example using kernel APIs:

intens_t_db = speos.client.intensity_templates()
intens_t_lamb = intens_t_db.create(
        message=ProtoIntensityTemplate(
            name="lambertian_180",
            description="lambertian intensity template 180",
            cos=ProtoIntensityTemplate.Cos(N=1.0, total_angle=180.0),
        )
    )
source_t_db = speos.client.source_templates()
thermic_source = source_t_db.create(message=ProtoSourceTemplate(name="thermic_source", description="thermic_source", thermic=ProtoSourceTemplate.Thermic(intensity_guid=intens_t_lamb.key, emissives_faces=ProtoSourceTemplate.Thermic.EmissiveFaces(temperature=2000.0))))