feat: Add ES6 parser and interpreter runtime support

[sharjeelyunus]

Description

This PR introduces comprehensive ES6 Phase 1 parser and interpreter runtime support. It expands the scripting capabilities of Ensemble by enabling block-scoped variables (let/const), template literals, destructuring declarations/assignments, default and rest parameters, spread operators, optional chaining, nullish coalescing, symbols, and non-blocking async/await execution.

Additionally, it adds detailed architecture and design documentation for both packages and resolves pre-existing analyzer and testing configuration issues.

Related Issue

None (N/A)

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)

What Has Changed

1. Parser Upgrades (packages/parsejs_null_safety)

• ES6 AST Nodes: Introduced AST structures for ForOfStatement, DefaultParameter, RestParameter, ObjectPattern, ArrayPattern, SpreadExpression, TemplateLiteral, TaggedTemplateExpression, and AwaitExpression.
• Lexer & Scanner: Added templates, optional chains (?.), and nullish coalescing (??) token scanning.
• Scope Annotation: Updated EnvironmentBuilder and Resolver to resolve scopes for destructuring binding targets, rest parameters, and default values.
• Test Utility Cleanup: Renamed helper scripts lexer_test.dart/parser_test.dart to lexer_tool.dart/parser_tool.dart to prevent the unit test runner (flutter test) from failing on parameter signatures.
• Analyzer Fixes: Updated ast_json.dart to replace unnecessary NaN checks with .isNaN and return null in empty visitor signatures.

2. Runtime Support (packages/ensemble_ts_interpreter)

• Lexical Scoping & TDZ: Built block-level scoping context stacks. Variables declared with let/const now enforce Temporal Dead Zone checks and const reassignment prevention.
• Loop Closures: Enabled loop iteration-specific contexts to ensure nested callback closures capture correct iteration snapshots.
• Optional Chaining & Coalescing: Integrated runtime optional chaining short-circuit evaluation and strict logical nullish check defaults.
• Type Semantics: Introduced jsUndefined (mapping out-of-bounds list accesses to JavaScript undefined rather than Dart null). Exposed Dart methods as closures to support callback references.
• Promises & Async/Await: Implemented async function execution wrapping using native Dart Future conversions.
• Global Polyfills: Added Promise.all/allSettled/race/any/finally, Array.from/of, and Object.fromEntries/hasOwn/getOwnPropertyNames.

3. Package Documentation

• Added packages/parsejs_null_safety/doc/parser_design.md (covers lexing, grammar hierarchy, visitor traversal, and scope resolution design).
• Added packages/ensemble_ts_interpreter/doc/architecture.md (covers block-scoped context engines, type marshaling, invokable schemas, async loops, and polyfills).

How to Test

1. Bootstrapped the monorepo packages:

   melos bootstrap

2. Ran unit tests for the parser:

   cd packages/parsejs_null_safety
   flutter test

   (41 tests pass successfully)
3. Ran unit tests for the runtime interpreter:

   cd packages/ensemble_ts_interpreter
   flutter test

   (319 tests pass successfully)

Screenshots / Videos

N/A (Backend Core Packages)

Checklist

• I have run flutter analyze and addressed any new warnings
• I have run flutter test and all tests pass
• I have tested my changes on the relevant platform(s)
• I have updated documentation if needed
• My changes do not introduce new warnings or errors

[cursor]

Bugbot is not enabled for your account, so this pull request was not reviewed.

Enable Bugbot in the Cursor dashboard to get automatic reviews on future PRs.