Replace triangular loader with blue circular spinner

[abansal15]

Description

Replaced the default triangular loader in PrefixHegemonyChart.vue and CountryHegemonyTable.vue with the blue circular spinner to maintain UI consistency across the site. Updated the corresponding CSS and markup without affecting functionality.

Related issue

#921

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[dpgiakatos]

This PR does not solve the corresponding issue; instead, it creates another issue. There are two loading effects in the modified components, and the spinner is not aligned with the position of the other loading components. Therefore, this PR should not be merged.

[dpgiakatos]

Please ensure that you have tested the changes before requesting a review.
Thanks.

[abansal15]

Hello @dpgiakatos can you please review it hopefully issue has solved now and sorry for the mistake i have done and will take care of it in the future .. actually i forgot to remove the Horizontal moving line which is along with Triangular loader causing multiple loading effect.. and also made the spinner at center

please see this image now spinner is at center and there is no Horizontal moving line..

[abansal15]

Also i have changed the equality check from == to === in the expression
return row.asn_name === '' ? '--' : row.asn_name
to enforce strict comparison. If you'd prefer to revert this change, please let me know.

[dpgiakatos]

Thanks