Feat/9 submodule size support

[envico801]

This PR adds support for displaying Git submodule sizes directly in the parent repository view.

Previously, submodules would always display ... because their paths point to a different repository and fail the normal tree lookup logic.

What changed

• Detect submodule links by checking whether the linked owner/repo differs from the current repository.
• Fetch the submodule repository tree and calculate the size using the same logic already used by the extension for normal repositories.
• Lazy load submodule sizes so the rest of the file list renders immediately without waiting for external requests.
• Cache in-flight requests to avoid duplicate API calls caused by GitHub rendering separate mobile/desktop anchors.

Submodules now initially render as Loading... and update automatically once the request completes.

This can be reproduced with:

• https://github.com/frida/frida/

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Files changed

• Added getExternalRepoSize() in api.ts
• Updated the main loop in dom-manipulation.ts

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Closes #9

Before:

After:

[envico801]

Worth mentioning that submodules are not considered in the total size sum of the parent repository, as they are references basically