[Schema] Fix Implementation::fromArray rejecting falsy-but-valid name/version

[DevkumarPatel]

Fixes #392.

Problem

Implementation::fromArray() validates the required name and version fields with empty(). Because empty('0') === true in PHP, a perfectly valid clientInfo/serverInfo carrying "version": "0" (or "name": "0") is rejected with an InvalidArgumentException.

During the initialize handshake this is especially confusing: the exception aborts parsing of the InitializeRequest, and Protocol::resolveSession() then reports the misleading error:

A valid session id is REQUIRED for non-initialize requests.

…which points nowhere near the actual cause.

Change

Replace the empty() guards with explicit checks:

if (!isset($data['name']) || !\is_string($data['name']) || '' === $data['name']) {
if (!isset($data['version']) || !\is_string($data['version']) || '' === $data['version']) {

This keeps rejecting the cases that should fail — missing, non-string, and genuinely empty ("") — while accepting falsy-but-valid strings like "0". Behavior is strictly widened; nothing previously valid is now rejected.

Tests

Adds tests/Unit/Schema/ImplementationTest.php (there was no existing test for this class), covering:

• Regression: "version": "0" and "name": "0" are accepted.
• Rejection of missing / empty-string / non-string name and version.
• Constructor defaults, minimal & full fromArray, non-array icons, and jsonSerialize round-trip.

OK (14 tests, 34 assertions)

vendor/bin/phpstan reports no errors on the changed file.

Scope note

The same empty()-on-required-string pattern exists in several sibling schema DTOs (Icon, Prompt, PromptArgument, ResourceDefinition, ResourceTemplate, Root, Tool) — e.g. a tool literally named "0" would hit the identical bug. I've kept this PR scoped to the reported issue; happy to follow up with a sweep (single PR or per-DTO) if you'd prefer.

[chr-hertel]

Thanks @DevkumarPatel for that patch - and follow-up for the broader scope very much welcome! 👍