ci: auto-tag and publish on version bump to main (AubaidFarrukh#48)

When a merge to main lands a package.json version with no matching
git tag yet, automatically create the tag and trigger the npm
publish workflow (workflow_dispatch, since a tag pushed by the
default GITHUB_TOKEN doesn't cascade into other workflow triggers).

PRs that don't bump the version are a no-op the tag already exists.

chore: prep repo for open-source contributions (AubaidFarrukh#22)

Make axios an optional peer dependency instead of a hard dependency,
and lazy-load it in AxiosRetry so fetch-only consumers aren't forced
to install it. AxiosRetry now throws a clear error at construction
time if axios is missing, instead of a bare "Cannot find module"
deep in a stack trace.

Add a CI workflow (lint/format/build/test across Node 18/20/22),
CONTRIBUTING.md, and a Contributor Covenant CODE_OF_CONDUCT.md.
Bump version to 1.0.4.

chore: add release scripts for versioning and tagging

Add preversion (run tests before allowing a bump), postversion (push
the commit + tag npm version creates), and a standalone tag script
that tags and pushes the current package.json version to trigger the
publish workflow.

Release v1.0.0: Initial stable release with @aubaid/smart-retry