fix typos in documentation and comments

[viktorking7]

This PR fixes minor spelling errors across the codebase:

- **docs/docs/noir/concepts/functions.md**: Fixed "pre-pended" → "prepended"
- **tooling/lsp/src/requests/completion.rs**: Fixed "trough" → "through" in comment
- **tooling/ssa_fuzzer/README.md**: Fixed "Condtion" → "Condition"

[github-actions]

Thank you for your contribution to the Noir language.

Please do not force push to this branch after the Noir team have started review of this PR. Doing so will only delay us merging your PR as we will need to start the review process from scratch.

Thanks for your understanding.