feat(pinia-orm)!: migrate to standard ECMAScript decorators

[CodeDredd]

What (breaking, targeted at 2.0.0)

Migrates all property decorators from the legacy experimentalDecorators implementation to the standard TC39 decorators that TypeScript supports natively since 5.0 (metadata since 5.2). With 2.0.0 being a major release, this is the right moment to require them.

Requirements for users

• TypeScript >= 5.2, experimentalDecorators removed from tsconfig (legacy calls hit a helpful error message at runtime)
• esbuild >= 0.21 / current Vite & Nuxt toolchains (they transform standard decorators out of the box)

Breaking changes in model definitions

before	after
@Attr('') declare name: string	@Attr('') name!: string
subclass override @Attr('dog') declare type: string	@Attr('dog') type = 'dog' (initializer, value unused)
@NonEnumerable hidden: string	@NonEnumerable accessor hidden: string
fields() models typed with field!: type	declare field: type (a real class field would wipe the hydrated value)

The docs Typescript guide is rewritten around these rules; all docs examples (37 pages), tests (38 files) and the nuxt3 playground are migrated.

How it works now

• New Metadata.ts: decorators write into decorator metadata (Symbol.metadata, polyfilled) — field factories, mutators, casts, hidden fields, onDelete modes. initializeSchema() consumes it.
• Field decorators return an initializer that keeps the hydrated value, so class fields (ES2022 useDefineForClassFields) no longer wipe what the Model constructor filled.
• Metadata inherits along the prototype chain (copy-on-write), so decorated fields of base classes are now inherited by derived STI models — that never worked with the legacy entity-keyed registry.
• Legacy invocation (with experimentalDecorators still on) throws a descriptive error instead of failing silently.

Behavior note

Extended models on the same entity (class ExtendedUser extends User without own entity) must be registered before the base class boots the entity — registration is now per class instead of leaking into a shared entity registry (adjusted in the has-many-through spec).

Verification

• Full suite green: 427 pinia-orm + 25 axios tests (every test exercises the new decorators — 38 spec files migrated)
• dts build, lint, size (16.18 kB / 16.5 kB) green
• tsc --noEmit error count identical to baseline (53, all pre-existing)

Not merged on purpose — please review, this is the biggest 2.0.0 breaking change.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.34%. Comparing base (b1fdd17) to head (319a3f3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2045      +/-   ##
==========================================
+ Coverage   99.29%   99.34%   +0.05%     
==========================================
  Files          82       83       +1     
  Lines        3100     3185      +85     
  Branches      559      562       +3     
==========================================
+ Hits         3078     3164      +86     
+ Misses         16       15       -1     
  Partials        6        6              

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