add `#[should_panic]` attribute expect options on `tests/*.rs`

[alejandro-vaz]

currently we use a ton of #[should_panic] attributes on our tests

most of them don't include an expect inside them, but some do. tests/bytes.rs:84:

#[should_panic(expected = "advance out of bounds: the len is 8 but advancing by 12")]
fn // ...

to make it consistent all #[should_panic] attributes on tests/*.rs should have an expect reason added to them

some of the exact errors are not deterministic, but the error type is, and since expect matches a substring it's easier to maintain if we just keep the error name without details

good example: "advance out of bounds"

bad examples:

• the full error with details: "advance out of bounds: the len is 8 but advancing by 12"
• no expect, just bare #[should_panic]
• anything that does not match the error name

[prakrititz]

I'd like to take this. Looks like tests/bytes.rs (2 sites) and tests/main.rs (6 sites) — I'll run each one to read the actual panic message and use the error-name substring rather than the full detail text, so e.g. "advance out of bounds" not the len/advancing specifics. Happy to leave it if someone's already started.

[alejandro-vaz]

alright take it, but know that AI contributions are not allowed in any @servo repository

https://book.servo.org/contributing/getting-started.html#ai-contributions

[prakrititz]

cool , thank you