[jibranshaikh0]

Description of the change

Resolves #150.

Adds None, Inherit, Initial, and Unset instances for Transformation, so
transform none, transform inherit, transform initial, and transform unset
render transform: none, transform: inherit, transform: initial, and
transform: unset, all valid values of the transform property per the MDN
reference linked in the issue (inherit, initial and unset are CSS-wide
keywords; none is specific to this property).

The instance shape follows the repository's existing pattern for BoxShadow in
src/CSS/Box.purs, adapted with an explicit Transformation $ fromString "..."
wrapper because Transformation has no IsString instance. TransformOrigin
intentionally receives no None instance, since transform-origin does not
accept none.

A new test/CSS/TransformSpec.purs asserts the exact rendered output for all
four keywords and is wired into test/Main.purs, and a changelog entry is added
under "Unreleased" -> "New features".

---

Checklist:

• Added the change to the changelog's "Unreleased" section with a link to this PR and your username (entry added citing Transform lacks None, Inherit, Initial, and Unset instances #150 and @jibranshaikh0; the PR link will be added once the PR number exists)
• Linked any existing issues or proposals that this pull request should close — resolves Transform lacks None, Inherit, Initial, and Unset instances #150
• Updated or added relevant documentation in the README and/or documentation directory (N/A: no documentation changes needed)
• Added a test for the contribution (if applicable) — TransformSpec asserts the exact rendered CSS for all four keywords

Testing (exact scope)

Verified by automated validation in a clean checkout with the repository's own CI
commands (Node 22, purescript 0.15.16, spago 1.0.5, purs-tidy):

• spago build --strict — passes with no warnings or errors
• spago test — passes; the new spec confirms transform: none,
  transform: inherit, transform: initial, and transform: unset render
  exactly
• purs-tidy check src test — passes

Verification is at the compiler and test-suite level only, matching how this
library is consumed (a compile-time DSL). No downstream application was built
with the patched library, and no manual testing beyond the automated suite
above was performed.

AI assistance disclosure: the implementation, tests, and this PR description
were prepared with AI assistance.