Adds more useful output for invalid UTF8 error.

[xhain]

When using the typheshare-cli I got an error notifying me of a file that has invalid UTF8 encoding:

thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: Error { kind: InvalidData, message: "stream did not contain valid UTF-8" }', cli/src/main.rs:264:58

I still had to manually backtrace which file was affected, so I implemented a more useful error message for this case that additionally lists the file path:

thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: "/project/core/._nonUTF8file.rs, stream did not contain valid UTF-8"', cli/src/main.rs:264:98

[Lucretiel]

Instead of unwrapping a string, recommend just unwrap_or_else with a panic:

std::fs::read_to_string(filepath)
    .unwrap_or_else(|e| panic!("failed to read file at {filepath:?}: {e}"))

[xhain]

Thanks for the suggestion! I updated the change to use this pattern.

[Lucretiel]

Thanks for you contribution! Left a small comment but this should be an easy merge once fixed

[Lucretiel]

Looks great!

[xhain]

Updated all 4 commits, as I forgot to sign the them.