tracing-appender & examples/: bump thiserror to "^2"

[LeoniePhiline]

Feature Request

thiserror 2.0.0 has been released.

Commonly, no code migration is necessary.

Crates

• tracing-appender
• tracing/examples/

Motivation

Updating to v2 reduces compile time for projects keeping up to date, as only one single version of thiserror must be compiled.

Proposal

Bump thiserror to v2.

Alternatives

Keep v1. However, updating is very simple (no code changes expected), and v1 should no be expected to receive further minor updates.

Difficulty

Good first issue.