fix(form): correctly handle Map and POJO types

[EduardoRadieske]

Description

Fix form encoding for Map and POJO types by improving type detection.

Changes

• Improve POJO detection for parameterized types.
• Prevent Map, collection, primitive, and array types from being treated as POJOs.
• Ensure non-Map JDK types are delegated to the default encoder.
• Add and update tests covering Map, collection, primitive, array, POJO, and parameterized type handling.

Testing

Added and updated unit and end-to-end tests covering the affected form encoding paths.

Related issue: #2827

[velo]

Thanks for the fix. A couple of things before this can go in:

Blocking

1. PojoUtil.isUserPojo(Class) calls type.getPackage().getName(), but getPackage() returns null for arrays and primitives. A form-encoded method with a byte[] or int body now throws an NPE in FormEncoder.encode. With createPredicatedFormEncoder() the predicate throws instead of returning false, so the request never reaches the delegate encoder. Please return false for primitives, arrays, and classes with no package, and add a test for each.
2. WildCardMapTest.testMapStringString already passes on master, because FormEncoder.encode and the formRequests predicate check instanceof Map before calling isUserPojo. So it doesn't cover the fix. The real improvement is non-Map JDK types (e.g. a List<String> body or a raw interface type) no longer being treated as POJOs. Please add an end-to-end test through FormEncoder for that case.

Nits

• FormEncoder.isMap(Object) only wraps instanceof Map; inline it.
• Please revert the unrelated changes: the javadoc <pre> reformat, and the appendToFile removal, which leaves the @TempDir logDir field unused.
• The test package is feign.form.utils, but the main package is feign.form.util.
• PojoUtilTest.TypeReference writes java.lang.reflect.ParameterizedType in full even though it's already imported.

[EduardoRadieske]

Thanks for the review. Addressed the requested changes and updated the tests.

I kept appendToFile removed because it causes TempDir cleanup failures on Windows: log.txt remains open when JUnit tries to delete the temporary directory. Since logDir is no longer used, I also removed the unused TempDir field.