Fix schema resolution when $id base URI differs from the loaded schema URI

[shin19991207]

What does this PR do?

The regression was introduced in #1186, where the added _preferLocalBaseForRemoteId sets a schema node’s baseUri to the local file path when a schema is loaded from a local file whose root $id ends with the same filename. In this case, the resolver effectively treated the local file URI as the base for resolving relative references.
This behavior caused problems for embedded resource resolution. Because the resolver used the local file URI as the effective base, relative references could resolve against the wrong location. In particular, embedded resource references failed because resourceIndexByUri stores embedded resources under their original $id, not under a locally rewritten URI. As a result, internal references such as #/$defs/... could not find a corresponding item in resourceIndexByUri and thus could no longer be resolved correctly.

The fix separates the schema’s logical resolution base from the source URI it was loaded from. This removes the behavior that preferred a same-named local file as the effective base for a remote $id. Instead, the resolver now keeps these concerns distinct and only uses the source URI as a fallback when resolving external references to local sibling files. Now, we have:

• _baseUri: the logical resource URI derived from the schema’s $id
• _sourceUri: the URI of the file the schema was loaded from
  This separation ensures that logical resolution remains consistent with the schema’s $id, while still allowing the source URI to be used for local file resolution.

What issues does this PR fix or reference?

Fixes #1236

Is it tested? How?

• Manual test from Bundled schema resolution fails for schemas with $id matching a file name #1236
• Automated tests

[datho7561]

Looks good and addresses the linked issue. Thanks, Morgan!