No source could render the map.
Returned when a render has fallback sources and every one failed, or when a source was
skipped because its circuit breaker is open. :attempts lists each source in the order
it was tried, with the StaticMaps.TileError it failed with, or :circuit_open if it
was skipped.
A render with a single source whose tiles fail returns the StaticMaps.TileError
itself.
Summary
Types
@type t() :: %StaticMaps.UnavailableError{ __exception__: term(), attempts: [{module(), StaticMaps.TileError.t() | :circuit_open}] }