chore: add changelog and update README for fix/remove-librs

[Copilot]

Short summary:

• Adds README.md and CHANGELOG.md (CHANGELOG.md already committed) to document the recent cleanup & snapshot updates performed on branch fix/remove-librs.

Details:

• Exported io module (atomic) and made various cleanup changes related to removing library references.
• Updated glyph formatting snapshot after running cargo insta review and accepting the new snapshot.
• All tests passed locally (34 unit tests and multiple integration/golden tests; snapshots reviewed).

Notes & next steps for reviewers:

• CI should be allowed to run and verify platform-specific behavior.
• There are small non-critical compiler warnings (unused variables, dead method) that should be addressed in a follow-up.

Target branch: main
Source branch: chore/update-changelog-readme
Commit message: chore: add README.md and PR for changelog/readme updates

Please create the PR and push README.md to the existing branch. Do not merge; leave for review.

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