consistent logging to enable better debugging

[insipx]

Makes logging more consistent by only using the tracing crate wherever possible. the tracing crate provides contextual tracing useful for debugging async code, but can also fallback to emitting log events if no subscriber is set.

• removes tracing-test crate preferring a small custom closure to capture logs from tests instead
  • this closure only works with tokios current_thread runtime. It can be made to work with a multi-thread environment, but not needed since its only used in a couple places so far. could make use of tracing-subscriber reload handle with rusts LazyLock global initializer to temporarily switch out a custom global subscriber that logs to a internal memory buffer only in the closure.
  • removing this allows us to avoid setting the traced-test global subscriber in ctor, giving us the ability to filter logs during debugging
• Default log level for tests is still INFO
• Logs in tests can be filtered on module again, which is useful for debugging
  • EX: if i'm debugging something related to sync, I can do RUST_LOG=xmtp_mls::groups=DEBUG to only get logs from xmtp_mls/src/groups/mod.rs
• tracing also has useful adapters for debugging WebAssembly code
• removes env_logger from mls_validation service preferring tracing-subscriber

bindings_ffi still uses the log crate. The FfiLogger trait doesn't fit well into the tracing::Subscriber trait -- enabling tracing there could be a different issue/PR but for now the benefit would be small to switch it out

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[codabrink]

Thank you!