Support plain userinfo in ss URLs

[TurboTheTurtle]

Summary:

• Accept plaintext percent-encoded userinfo in ss:// URLs.
• Keep the existing base64 userinfo path for backward compatibility.
• Add coverage for an AEAD 2022 URL containing a percent-encoded base64 key.

Why:
ssurl can emit ss://method:password@host:port links where the userinfo is percent-encoded rather than base64-wrapped. The Android importer only tried base64-decoding that userinfo, so valid AEAD 2022 links failed to import.

Closes #3135.

Validation:

• git diff --check
• JAVA_HOME=/opt/homebrew/opt/openjdk@21 ANDROID_HOME=/Users/andy/Library/Android/sdk ./gradlew :core:compileDebugKotlin
• JAVA_HOME=/opt/homebrew/opt/openjdk@21 ANDROID_HOME=/Users/andy/Library/Android/sdk ./gradlew :core:connectedDebugAndroidTest -Pandroid.testInstrumentationRunnerArguments.class=com.github.shadowsocks.database.ProfileTest

Please preserve author attribution if this PR is squashed or reworked:
Co-authored-by: Andy Ye 35905412+TurboTheTurtle@users.noreply.github.com