Add ByteTables module and bench_quick.rb benchmark harness

ByteTables provides pre-computed 256-entry boolean lookup arrays for
byte classification (IDENT_START, IDENT_CONT, WORD, DIGIT, WHITESPACE)
and named constants for delimiter bytes (NEWLINE, DASH, DOT, HASH).

bench_quick.rb measures parse µs, render µs, and object allocations
for the theme benchmark suite.

lib/liquid.rb

@@ -52,6 +52,7 @@ end
 require "liquid/version"
 require "liquid/deprecations"
 require "liquid/const"
+require "liquid/byte_tables"
 require 'liquid/standardfilters'
 require 'liquid/file_system'
 require 'liquid/parser_switching'