enable opting-out of thrown Error tracing

[tayloraswift]

Description

follow up from Slack: https://swift-open-source.slack.com/archives/C06QXFKB4ER/p1730243185369769

running tests with Testing, even in -c release mode, results in an >100x slowdown when using certain libraries such as swift-json due to the way it parses UTF-8 text internally. this in turn is because swift-grammar, which swift-json’s parser is implemented in, throws an Error on nearly every input character.

Expected behavior

there should be a way to locally disable Error tracing so we can use these libraries within test runners.

Actual behavior

it takes many minutes to parse a large JSON file within a test runner, which should only take a couple seconds.

Steps to reproduce

tayloraswift/swift-json#80 demonstrates the problem

swift-testing version/commit hash

6.0.1

Swift & OS version (output of swift --version ; uname -a)

No response

[grynspan]

@tayloraswift and I discussed this in Slack briefly. It'd be great if you can get some backtraces from during the hang so we can confirm the theory before we make a speculative change.