Element-R: support for manual import/export of Room keys (#3364)
* Rust manual import/export for keys
* code review
* code review
* post merge fix
* code review
* doc: comma splice
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
* Better test name
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
* quick doc update
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
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Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>