Optimize MessageBus::Client#allowed? method

[moberegger]

This was coming up as a memory allocation hotspot in our production profiles, specifically the - operation when calculating group_allowed. Luckily there is a very easy optimization here: simply use intersect?! This performs the same check with zero additional memory allocation.

I ran some benchmarks against the allowed? method. I was expecting this optimization to get diluted in the larger method body, but the results look good.

allowed? now allocates no additional memory

Calculating -------------------------------------
                main    40.000  memsize (     0.000  retained)
                         1.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)
           optimized     0.000  memsize (     0.000  retained)
                         0.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)

Comparison:
           optimized:          0 allocated
                main:         40 allocated - Infx more

Not only that, it is 1.77x faster!

ruby 4.0.2 (2026-03-17 revision d3da9fec82) +YJIT +PRISM [arm64-darwin25]
Warming up --------------------------------------
                main   558.220k i/100ms
           optimized   967.314k i/100ms
Calculating -------------------------------------
                main      6.551M (± 2.3%) i/s  (152.66 ns/i) -     32.935M in   5.030441s
           optimized     11.626M (± 3.4%) i/s   (86.02 ns/i) -     59.006M in   5.082509s

Comparison:
                main:  6550535.1 i/s
           optimized: 11625658.9 i/s - 1.77x  faster

I would expect the improvement to be more profound in a production scenario because the call sites to the allowed? method both happen in a loop; one iterating over messages, another over subscriptions.