fix(streaming-shared): validate range response metadata

[dajiaohuang]

Summary

• validate declared Content-Range and Content-Length metadata independently of the option that requires a non-redirected response to use status 206
• preserve the specific mismatch reason in FetchLoader errors
• add FetchLoader and XhrLoader regression coverage for inconsistent Content-Length values

Fixes #1941

Tests

• node %TEMP%\xgplayer-audit-2c4e5f6-node_modules\jest\bin\jest.js packages/xgplayer-streaming-shared/__tests__/net/fetch.spec.js packages/xgplayer-streaming-shared/__tests__/net/xhr.spec.js --runInBand --ci --verbose=false --forceExit (10 passed)
• node %TEMP%\xgplayer-audit-2c4e5f6-node_modules\jest\bin\jest.js --runInBand --ci --verbose=false --silent --forceExit (52 suites, 302 tests passed)
• biome lint packages/xgplayer-streaming-shared/src/net/fetch.js packages/xgplayer-streaming-shared/src/net/xhr.js packages/xgplayer-streaming-shared/__tests__/net/fetch.spec.js packages/xgplayer-streaming-shared/__tests__/net/xhr.spec.js --diagnostic-level=error --max-diagnostics=100
• git diff --check