Stop byteslicing empty strings in breadcrumbs

[nirebu]

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Description

Describe your changes:

If we don't pass a message to the breadcrumb message, we default to an empty string. However we can avoid byteslicing it, which allocates a new empty string every time regardless.

This is a pretty hot path, and the tests pass. Only difference I can think of is returning a frozen empty string, which could cause issues downstream. Let me know if it should be dup-ed!

require 'benchmark-memory'

MAX_MESSAGE_SIZE_IN_BYTES = 1024 * 8

def current(message)
  (message || "").byteslice(0..MAX_MESSAGE_SIZE_IN_BYTES)
end

def updated(message)
  message ? message.byteslice(0..MAX_MESSAGE_SIZE_IN_BYTES) : ""
end

Benchmark.memory do |x|
  x.report("current") do
    current(nil)
  end

  x.report("updated") do
    updated(nil)
  end

  x.compare!
end

Calculating -------------------------------------
current 80.000 memsize ( 0.000 retained)
2.000 objects ( 0.000 retained)
1.000 strings ( 0.000 retained)
updated 0.000 memsize ( 0.000 retained)
0.000 objects ( 0.000 retained)
0.000 strings ( 0.000 retained)

Comparison:
updated: 0 allocated
current: 80 allocated - Infx more