#2 stub WTS HTTP calls with webmock

[kreinba]

Issue #2 asks for webmock-based unit tests because the existing suite reaches the live WTS at https://wts.zold.io for every test. The existing tests call WebMock.allow_net_connect!, so any failure or latency on the third-party host produces a red CI run, and the suite cannot be relied on as a unit-level signal for the code in lib/zold/wts.rb.

This change replaces the live calls in test/zold/test_wts.rb with webmock stubs covering /pull, /job?id=..., /balance, /id, /find?..., and /usd_rate, and moves WebMock.disable_net_connect! into a setup hook so no test can leak to the network. The eight existing tests still cover the same code paths in Zold::WTS and Zold::WTS::Fake, but each one now finishes in milliseconds and never depends on wts.zold.io being reachable.

Locally on Ruby 3.3.6: bundle exec rake test runs all 8 tests in under one second with 0 failures and 86.67% line coverage; the previous run on master took roughly 24 seconds against the live host. The rake rubocop step exhibits the same rubocop-rspec_rails inject_defaults! failure as master, so this branch does not introduce a new lint failure.

Closes #2

[edmoffo]

Closes #2 cleanly. Each of the eight existing tests in test/zold/test_wts.rb now runs against a webmock stub for the WTS endpoint it touches, and setup pins WebMock.disable_net_connect! at the class level so no test can leak to wts.zold.io. Local bundle exec rake test runs all 8 tests in 0.03s with 0 failures and 86.67% line coverage, matching the numbers in the PR body. The four red CI checks on this branch (rubocop-rspec_rails inject_defaults, markdown-lint on README.md, criterias typo, yamllint) are also red on master at 7c79029, so this diff does not introduce them. No inline comments.