Return early from bootstraping symbols if paths are empty (#2078)

### Motivation

Another tiny improvement that I identified during studying memory dumps. When passing a constant list to Tapioca, we end up invoking `symbols_from_paths` with an empty array.

Currently, it will still create an empty tempfile and run Sorbet on it, which is unnecessary.

### Implementation

We can return an empty set directly if no paths are given.

lib/tapioca/static/symbol_loader.rb

@@ -51,6 +51,8 @@ def gem_symbols(gem)
 
         sig { params(paths: T::Array[Pathname]).returns(T::Set[String]) }
         def symbols_from_paths(paths)
+          return Set.new if paths.empty?
+
           output = Tempfile.create("sorbet") do |file|
             file.write(Array(paths).join("\n"))
             file.flush