What this PR does / why we need it:

Fixes a handful of small wording issues in the docs, including duplicated words, article usage, spelling of "separate", and one sentence that referenced three approaches after listing four.

Which issue(s) this PR fixes:

N/A

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests
• Integration tests
• Manual tests
• Testing is not required for this change

Manual checks:

• git diff --check
• rg -n "a a tool|seperate|by the the|a example|no exception were|These three approaches|multiple entities are a subclass" docs/getting-started docs/reference docs/tutorials

Misc

Docs-only cleanup; no behavior changes.