Reject stream URLs without a scheme during URL validation

[blihio]

Problem

UrlParser.parse("//localhost/live/test", arrayOf("rtmp")) passes host/path validation but throws NullPointerException when the null scheme is assigned to a non-null Kotlin property.

The streaming clients catch URISyntaxException during URL validation, so this input bypasses their malformed-endpoint handling.

Change

Reject a missing scheme along with unsupported schemes using the existing URISyntaxException path.

Add two regression cases to UrlParserTest: a scheme-less hostname URL and a scheme-less IPv4 URL with an explicit port. Both fail with NPE before the fix and pass afterward.

Validation

With only this change applied to base commit 82a9cb4ee4babdc792d2ccee8b893f2b36207d40, using Gradle 9.7.1 and JDK 17:

./gradlew :common:testDebugUnitTest :encoder:testDebugUnitTest

• common: 100 tests passed, including the existing URL parsing tests.
• encoder: 25 tests passed.
• git diff --check passed.

Fixes #2218

[pedroSG94]

Thank you for the PR. Merged