Check a base URL against every rule of baseUrlProblem — blank, whitespace
or control characters, not an absolute URL, a scheme other than http:/https:,
a query or fragment — and return it with trailing slashes stripped. A bad value
throws a MastrValidationError (Invalid baseUrl: <reason>): it is a configuration
error, not a transport failure. The default transport still gates the scheme per
request, but the engine may be handed a custom transport that does no such check,
so the configured value is checked here, on the raw string.
Check a base URL against every rule of baseUrlProblem — blank, whitespace or control characters, not an absolute URL, a scheme other than
http:/https:, a query or fragment — and return it with trailing slashes stripped. A bad value throws a MastrValidationError (Invalid baseUrl: <reason>): it is a configuration error, not a transport failure. The default transport still gates the scheme per request, but the engine may be handed a custom transport that does no such check, so the configured value is checked here, on the raw string.