Optimize light configuration and caching

[bolshakov]

Improved System#light caching performance using pre-computed configuration digests and added better error messages with source locations.

• Pre-compute digest during LightConfigurationDsl initialization
• Implement #hash for traffic/recovery control strategies -- allows comparing configurations effectively
• Cache UNDEFINED constant (saves Undefined.instance lookup overhead) - there is more room for improvement here, but it does not play well with RBS.
• Improve configuration conflict errors. Previously error message included both configurations, not it includes both call sites.
• Split DSL classes by use case
  • LightConfigurationDsl: Optimized for light caching with pre-computed digest
  • SystemConfigurationDsl: For system-level configuration
  • LegacyConfigurationDsl: For backward compatibility, used outside of system, will be removed eventually.

Performance impact

More effective lights cashing enabled a massive performance gain on light lookup.

ruby 3.2.4 (2024-04-23 revision af471c0e01) [arm64-darwin23]
Warming up --------------------------------------
               after    70.405k i/100ms
Calculating -------------------------------------
               after    690.021k (± 3.8%) i/s    (1.45 μs/i) -      3.450M in   5.007544s

Comparison:
               after:   690021.2 i/s
              before:   251477.5 i/s - 2.74x  slower

When we switch to "system lights", a hottest path will have a very little overhead for light instantiation:

Stoplight(name).run {. ... } # <- Faster lookup