refactor!: rework core api

[tisonkun]

See changelog updates.

[Copilot]

Pull request overview

This PR refactors the core API to change how log message payloads are handled throughout the logging framework. The primary change is replacing string-based payloads with std::fmt::Arguments<'a>, which allows for zero-cost formatted message handling by deferring string allocation until necessary.

Key Changes:

• Changed Record payload from OwnedStr to fmt::Arguments<'a> to avoid unnecessary string allocations
• Removed OwnedStr and RecordOwned types from the core library (moved RecordOwned to async worker)
• Replaced crossbeam-channel with std::sync::mpsc in the async appender to reduce dependencies

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
core/src/record.rs	Changed payload type from OwnedStr to fmt::Arguments<'a>, removed RecordOwned, added time() and column() builder methods
core/src/str.rs	Removed OwnedStr type and its into_owned() method, added into_cow_static() to RefStr
core/src/kv.rs	Updated KeyOwned to use Cow<'static, str> instead of OwnedStr
layouts/logfmt/src/lib.rs	Adapted to handle fmt::Arguments payload by converting to Cow<str>
layouts/json/src/lib.rs	Changed RecordLine.message to fmt::Arguments<'a> for direct serialization
layouts/google-cloud-logging/src/lib.rs	Changed RecordLine.message to fmt::Arguments<'a> for direct serialization
bridges/log/src/lib.rs	Simplified payload handling by directly passing fmt::Arguments
appenders/opentelemetry/src/lib.rs	Updated to call to_string() instead of to_owned() on payload
appenders/journald/src/field.rs	Added PutAsFieldValue implementation for fmt::Arguments<'_>
appenders/fastrace/src/lib.rs	Adapted to convert payload to Cow<str>
appenders/async/src/worker.rs	Moved RecordOwned into this module and adapted to reconstruct records from owned data
appenders/async/src/state.rs	Updated error types from crossbeam_channel to std::sync::mpsc
appenders/async/src/lib.rs	Implemented custom Sender enum to wrap both bounded and unbounded channels
appenders/async/src/append.rs	Updated to use new Sender type and RecordOwned::from_record()
appenders/async/Cargo.toml	Removed crossbeam-channel dependency
Cargo.toml	Removed crossbeam-channel from workspace dependencies
appenders/file/tests/global_file_limit.rs	Updated tests to use format_args!() instead of format!()

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