Allow @encode(string) on boolean, define case-insensitive true|false string semantics, and add Spector coverage

[Copilot]

@encode(string) was restricted to numeric targets, blocking APIs that model booleans as strings (for example "true" / "false" in payloads or query values). This change extends support to boolean targets, clarifies the docs contract, and adds http-specs Spector coverage.

• Compiler validation

  • Relaxed @encode validation so the implicit string encoding path (@encode(string)) is valid for boolean in addition to numeric.
  • Updated related diagnostic wording to reflect numeric-or-boolean applicability.

• Standard library/docs contract

  • Updated @encode decorator docs to state boolean string encoding uses case-insensitive true / false values.
  • Added a boolean-focused @encode(string) example.
  • Removed parsing-specific wording from the boolean string semantics text.

• Coverage

  • Added a focused compiler decorator test that validates @encode(string) on a boolean model property.
  • Updated the non-supported-type expectation to match the new allowed target set.
  • Added/updated Spector coverage in packages/http-specs/specs/encode/boolean with matching mock API and regenerated packages/http-specs/spec-summary.md.
  • Boolean property scenarios now cover multiple casings/values via:
    • /encode/boolean/property/true-lower
    • /encode/boolean/property/false-lower
    • /encode/boolean/property/true-upper
    • /encode/boolean/property/false-mixed
  • Updated boolean mock API request validation to use an asymmetric matcher so request boolean-string values are accepted case-insensitively (true/false), while still returning varied response casings for coverage.

model FeatureFlags {
  @encode(string)
  enabled: boolean;
}

[timotheeguerin]

@copilot add a spector test in http-specs packages

[Copilot]

Added in 8237396.