feat: allowlist enum method invocation and return types

[jasmith-hs]

Description

This PR description was authored by Claude Code.

jinjava sandboxes template rendering with two allowlists — a method allowlist and a return-type allowlist — both of which match a value's canonical class name against configured names/prefixes.

A simple enum (enum Color { RED, GREEN }) could already be allowlisted by adding its canonical class name. But an enum with a constant-specific class body (enum Op { PLUS { int apply(){...} } }) is realized at runtime as an anonymous subclass (Op$1) whose getCanonicalName() returns null. Both validators bail on a null canonical name, so these enums — their values and their overridden methods — could never be allowlisted, even when the caller explicitly added the enum type.

This change resolves the runtime enum-constant class to its base enum type before the existing canonical-name check, so allowlisting a specific enum by class name works for its values and methods, including constant-specific bodies.

Scope is intentionally narrow: specific enums only. No blanket "allow all enums" toggle, no new builder helper, no new AllowlistGroup — just correct resolution of the value/method class back to the enum type the caller already allowlisted.

• AllowlistReturnTypeValidator: when the value is an enum, validate against ((Enum<?>) o).getDeclaringClass() instead of the runtime class.
• AllowlistMethodValidator: when a method's declaring class has a null canonical name and its superclass is an enum, use the enum type's canonical name for the check.

Both are no-ops for simple enums and non-enum values.

BRAVE

Backwards Compatibility

• Fully backwards compatible.
• No API changes; the two validators only change how they derive the class name used for the existing allowlist check.
• No-op for simple enums and all non-enum values — behavior only changes for enum values that were previously rejected due to a null canonical name.

Rollout and Rollback Plan

• Standard library release; no data migration or feature gate.
• Rollback is a straight revert of this commit.

Automated Testing

• New AllowlistEnumTest (9 tests): direct validator checks for a simple enum and a constant-specific-body enum, rejection of a non-allowlisted enum (java.time.Month), and end-to-end renders ({{ op.apply(2, 3) }} → 5, {{ color.label }}, {{ op }} → name). The constant-body method test pins the regression by asserting the declaring class canonical name is null.
• New test enums SimpleColorEnum and OperationEnum under the already-allowlisted testobjects package.
• Full com.hubspot.jinjava.el.** suite (236 tests) passes; spotless:check clean.

Verification

• mvn -Dtest=AllowlistEnumTest,AllowlistGroupTest,ValidatorConfigBannedConstructsTest test — green.

Expect Dependencies to Fail

• None expected. The sandbox is only widened for enum types a caller has explicitly allowlisted; the @Value.Check guardrails still reject banned classes at config time, so resolution cannot expose anything not already permitted.

REVIEWERS: Please review both the code changes and the answers above, and validate that they match the expectations for BRAVE