PAYMENTS-12054 Fix the CI bundler cache and the puma spec port collisions

[WillemHoman]

Jira: PAYMENTS-12054

N.B. no Changelog updates as will have a release with #45

What? Why?

Fixes

1. restore_cache has been failing on every job of every build

template: cacheKey:1:24: executing "cacheKey" at <checksum "Gemfile.lock">:
error calling checksum: open /home/circleci/repo/Gemfile.lock: no such file or directory
error computing cache key

orbs/internal-ruby.yml builds its key as <cache_key>-{{ arch }}-{{ checksum <checksumfile> }}, and checksumfile
defaults to Gemfile.lock.

This repo ships no lockfile, it is gitignored so it always resulted in a cache miss.
The Gemfile is the stable file that does exist so it is used as the checksumfile.
Reduces the build by ~ 5 mins.

2. The puma specs collide on ports

default_port was 9800 + rand(100)

require 'spec_helper'

describe Bigcommerce::Prometheus::Servers::Puma::Server do
  let(:server) { described_class.new(port: default_port) }
  let(:default_port) { 9800 + rand(100) }

Constructing the server binds a real listener.
Three examples use it, so they collide about 3% of the time, raising an Errno::EADDRINUSE.

1. Bind ephemeral: Port 0 asks the kernel for a free port so two live listeners cannot share one.
2. Close on teardown: closes the port on spec teardown.

How was it tested?

CI

---

Note

Low Risk
CI and test-only changes with no production runtime behavior; low risk aside from verifying cache keys still isolate Ruby versions correctly.

Overview
Fixes CircleCI bundler cache restore failures and intermittent Puma server spec port collisions.

CI: Sets shared checksumfile: Gemfile (this repo has no committed Gemfile.lock) and distinct cache_key values per Ruby job (gem-cache-ruby-3_3, 3_4, 4_0) so the internal-ruby orb can compute cache keys without error and restore gems reliably.

Specs: Puma Server examples now bind port 0 for ephemeral listeners instead of 9800 + rand(100), track started servers, and close binders in an after hook. The configured-port example probes a free port via TCPServer on port 0 so assertions still target a known port without colliding with other examples.

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