Add method for generated interpreters without input

[ReubenJ]

Support the following use-case:

HerbInterpret.jl/test/make_interpreter_tests.jl

Lines 81 to 98 in 48a66e2

	g = @csgrammar begin
	Number = |(1:2)
	Number = x
	Number = Number + Number
	Number = Number * Number
	Number = Number + 1
	Number = x * 2
	end
	# Compile once
	interpret_custom = HerbInterpret.make_interpreter(g; input_symbols=[:x])
	rn = @rulenode(5{4{3,2},7}) # (x + 2) * (x * 2)
	input = Dict{Symbol,Any}(:x => 1)
	@testset "No input" begin
	@test interpret_custom(@rulenode(4{1,1})) == 2
	end

Additionally, relax the type bounds on the input argument for generated interpreters. Previously, it was Dict{Symbol,Any} matching only dictionaries with an explicit Any type for the values, where we actually wanted to allow for dictionaries with any type of value <:Any.

While we're at it, switch to ReTestItems.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.41%. Comparing base (b5a6c5c) to head (f3debbe).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #51      +/-   ##
==========================================
+ Coverage   69.11%   69.41%   +0.29%     
==========================================
  Files           3        3              
  Lines         204      206       +2     
==========================================
+ Hits          141      143       +2     
  Misses         63       63              

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[github-actions]

Benchmark Results

	master	f3debbe...	master / f3debbe...
interpret/Random Expressions	0.126 ± 0.0015 ms	0.126 ± 0.0017 ms	0.997 ± 0.018
time_to_load	0.0853 ± 0.0029 s	0.0848 ± 0.00054 s	1.01 ± 0.035

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).