New dictionary functions

[maurolepore]

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TODO

• [ ] Draft the PR title.
• [ ] Link related issue/PR.
• [ ] Draft the PR description.
• [ ] Mark the PR as draft.
• [ ] Include a unit test.
• [ ] Review your own PR in "Files changed".
• [ ] Ensure the PR branch is updated.
• [ ] Ensure all checks pass.
• [ ] Change the PR status from draft to ready.
• [ ] Polish the PR description to reflect it's goal (why not how).
• [ ] Polish the PR title as you'd like others to read it from the git log.
• [ ] Assign a reviewer.
• [ ] Update renv.lock (no init): fs::file_delete("renv.lock"); renv::snapshot().

Also if the PR includes user-facing changes:

• [ ] Increment the version number: fledge::update_version()
• [ ] Update the changelog: fledge::update_news()
• [ ] Merge then tag: fledge::tag_version()