Allow different types on with_meta arguments

[itsibitzi]

Before this change we constrained both the key and the value on with_meta to be the same type. This resulted in stuff like blah.with_meta("key", &value.to_string()), which is basically turning value from a T: ToString into a String into a &str and then inside the function back to a String again. Twice the allocation, twice the fun.

This PR ruins that fun by allowing the key and value to be different kinds of ToString.

This could be more idiomatic as a pair of impl Into<String> since that allows things like an owned string to not have to reallocate, but that would be a breaking change so this will perhaps do for now. Though ToString does allow anything with Display to also be used here which is maybe nice?

[Copilot]

Pull request overview

This PR removes an unnecessary type constraint in the with_meta method that previously required both key and value parameters to be the same type. The change eliminates redundant string conversions where callers had to convert values to strings just to satisfy the single generic type parameter.

Changes:

• Updated with_meta signature to accept two different ToString types instead of one
• Simplified call sites by removing unnecessary .to_string() conversions

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
crates/twirp/src/error.rs	Modified with_meta method signature to accept separate generic types for key and value
crates/twirp/src/server.rs	Removed redundant .to_string() calls when passing error values to with_meta

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[tclem]

Nice! Good fix.