fix: restore the missing Data.Array.ST.clone

[Unisay]

Problem

Upstream purescript-arrays v7.3.0 exports Data.Array.ST.clone, backed by the cloneImpl :: STFn1 (STArray h a) h (STArray h a) foreign. The fork tracks the 7.3.0 sources but carried neither the export nor the foreign, so code written against the registry package failed to compile against the fork ("Unknown value clone"). Found by the upstream diff of the purescript-lua/purescript-lua#186 audit, where this was the only missing value export in arrays.

Change

• src/Data/Array/ST.purs: restore clone/cloneImpl exactly as upstream declares them (export after thaw, declarations after thawImpl).
• src/Data/Array/ST.lua: bind cloneImpl to the existing copyImpl, the same independent copy thawImpl/freezeImpl already use, per the STFn convention: a 1-ary entry that performs the copy directly.
• test/regression/array_st.lua: the guard covers cloneImpl (copies, independent of the source). It was red against the old FFI (attempt to call field 'cloneImpl' (a nil value)) and is green after the fix.

Verification

scripts/test green (regression suites for ST and NonEmpty), luacheck --std lua51 --no-unused-args src/ clean, nix develop -c ./scripts/build links all seven modules. End-to-end check with a small program that thaws [1,2,3], clones it, and pokes the clone, built on set psc-0.15.15-20260713 with arrays overridden to this checkout: before the fix purs rejected it with "Unknown value clone"; with the fix it compiles and prints [1,2,3] then [99,2,3], so poking the clone leaves the source array intact.

Suggested release: patch (v7.4.3) plus a package-set bump.

Refs purescript-lua/purescript-lua#267.

[Copilot]

Pull request overview

Restores the missing Data.Array.ST.clone API in this PureScript→Lua arrays fork to match upstream purescript-arrays v7.3.0, fixing downstream compilation failures for code expecting Data.Array.ST.clone.

Changes:

• Re-add clone and its cloneImpl foreign to Data.Array.ST, matching upstream signatures and export ordering.
• Implement cloneImpl in Lua by reusing the existing copyImpl (same independent-copy path used by freezeImpl/thawImpl).
• Add a Lua regression guard asserting cloneImpl produces an independent copy.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/Data/Array/ST.purs	Reintroduces clone export and foreign cloneImpl with STFn1 wiring via runSTFn1.
src/Data/Array/ST.lua	Exposes cloneImpl = (copyImpl) consistent with existing freezeImpl/thawImpl behavior and FFI export wrapping requirements.
test/regression/array_st.lua	Adds regression coverage ensuring cloneImpl copies and is independent of the source table.
changelog.d/20260713_180352_st_clone.md	Documents the restoration of Data.Array.ST.clone and its Lua backing implementation.

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