Complete assertion and load test results

This release makes atra (Atrahasis CLI) report exactly what it checked, so a green pipeline means the checks behind it actually ran.

• Every assertion in a command runs. Chaining several -a flags now evaluates and reports each one, and any failure among them fails the command. Previously only the first expression in a chain was evaluated.
• Multi word assertion values are matched in full. -a "body contains user created" looks for the whole phrase rather than the first word.
• Load test thresholds reach the exit code. A spec whose thresholds are missed now exits non zero, so a load test can gate a pipeline the same way assertions do.
• --json is one parseable document. Assertion results are included inside it under assertions, with counts and per assertion detail, so the output can be piped straight into jq or any other tool.
• A base_url ending in a slash behaves as expected. Joining it with a path that starts with a slash no longer sends a doubled slash, which some servers route differently and reject.
• A mistyped flow or spec name says so. atra run -f logut now names the flow it could not find and lists what is available, instead of reporting that the folder holds nothing.
• An unknown random generator stops the run. A typo such as {{random.emial}} used to be sent to the server as literal text; it now fails immediately and names the mistake.
• Hints match the problem. A missing environment variable is no longer answered with a suggestion to check your network connection.

Some pipelines will report failures after upgrading that they did not report before. Those checks were being skipped, and the build was passing without them, so read the new failures as results you were not getting until now.

Nothing in your flows, specs or commands needs to change.