See #8222 for context.i
`GetBlobContentBase64` was using a pipe and a goroutine to read the blob content as base64. This can be replace by a pre-allocated buffer and a direct copy.
Note that although similar to `GetBlobContent`, it does not truncate the content if the blob size is over the limit (but returns an error). I think that `GetBlobContent` should adopt the same behavior at some point (error instead of truncating).
### Tests
- I added test coverage for Go changes...
- [x] in their respective `*_test.go` for unit tests.
- [x] I did not document these changes and I do not expect someone else to do it.
### Release notes
- [x] I do not want this change to show in the release notes.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8297
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: oliverpool <git@olivier.pfad.fr>
Co-committed-by: oliverpool <git@olivier.pfad.fr>
