feat(sorted_map): make trait promotions explicit via extend

[bobzhang]

Summary

Part of the per-package series migrating moonbitlang/core off implicit trait-method promotion (see #3849 for deque). This one covers sorted_map only.

Promote — plain pub extend	Deprecate — #deprecated(…, skip_current_package=true) + #doc(hidden)
Default	@quickcheck.Arbitrary, @debug.Debug, Eq, @json.FromJson, the whole Show trait, ToJson

• Show is deprecated for collections — SortedMap's Show impl is already #deprecated on main (→ @debug.Debug).
• ToJson/FromJson point to the @json.to_json / @json.from_json free functions; each deprecation message names the concrete replacement.
• #doc(hidden) on all deprecations, so pkg.generated.mbti gains only SortedMap::default.

Migrates sorted_map's own blackbox test off the now-deprecated .to_json() (→ @json.to_json(...)). Scoped to sorted_map/.

Verification

• moon check --deny-warn --target all — clean.
• moon test -p moonbitlang/core/sorted_map --target all — green (87×4).

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Signed-off-by: Codex CLI <codex@openai.com>

[coveralls]

Coverage Report for CI Build 5306

Coverage remained the same at 91.293%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	17400
Covered Lines:	15885
Line Coverage:	91.29%
Coverage Strength:	196792.46 hits per line

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💛 - Coveralls

[Copilot]

Pull request overview

Migrates the sorted_map package away from implicit trait-method promotion by making promotions explicit via an extends.mbt shim, aligning with the ongoing per-package migration series (as previously done for deque).

Changes:

• Enable +implicit_impl_as_method warnings for sorted_map to surface and prevent implicit promotion usage.
• Add an extends.mbt shim that explicitly promotes Default::{default} while deprecating (and hiding from generated interface) prior promoted trait methods like ToJson::to_json, @json.FromJson::from_json, Eq, Show, etc.
• Update sorted_map tests to use @json.to_json(...) / @json.from_json(...) instead of the deprecated promoted .to_json() method.

Reviewed changes

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

File	Description
sorted_map/pkg.generated.mbti	Reflects the newly promoted SortedMap::default() in the generated public interface.
sorted_map/moon.pkg	Enables +implicit_impl_as_method warnings for this package to enforce the migration.
sorted_map/map_test.mbt	Updates JSON roundtrip tests to use @json.to_json / @json.from_json instead of deprecated promoted methods.
sorted_map/extends.mbt	Introduces explicit trait promotions and hidden deprecations to replace implicit trait-method promotion.

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