Add optional tracing support with slog bridge

Add an optional "tracing" feature that enables a bridge between the
tracing crate and slog, allowing users to use tracing macros while
maintaining slog's structured logging and bunyan format output.

Key changes:
- Add optional tracing dependencies behind "tracing" feature flag
- Implement SlogTracingBridge that converts tracing events to slog records
- Preserve structured data types (numbers, booleans) in log output
- Use proper detection with tracing::dispatcher::has_been_set()
- Initialize bridge automatically when feature is enabled
- Add comprehensive tests for bridge functionality

The bridge maintains backwards compatibility - existing slog usage
continues to work unchanged, and tracing is only available when
explicitly enabled via the feature flag.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: nshalman

Cargo.lock

@@ -43,6 +43,8 @@ slog-async = "2.8.0"
 slog-bunyan = "2.5.0"
 slog-json = "2.6.1"
 slog-term = "2.9.1"
+tracing = { version = "0.1.40", optional = true }
+tracing-subscriber = { version = "0.3.18", features = ["env-filter"], optional = true }
 thiserror = "2.0.12"
 tokio-rustls = "0.25.0"
 toml = "0.8.23"
@@ -136,6 +138,7 @@ version_check = "0.9.5"
 [features]
 usdt-probes = ["usdt/asm"]
 internal-docs = ["simple-mermaid"]
+tracing = ["dep:tracing", "dep:tracing-subscriber"]
 
 [package.metadata.docs.rs]
 features = ["internal-docs"]

dropshot/Cargo.toml

@@ -946,6 +946,8 @@ pub use server::ServerBuilder;
 pub use server::ServerContext;
 pub use server::ShutdownWaitFuture;
 pub use server::{HttpServer, HttpServerStarter};
+#[cfg(feature = "tracing")]
+pub use tracing::{debug, error, info, trace, warn}; // Re-export tracing macros for convenience
 pub use versioning::ClientSpecifiesVersionInHeader;
 pub use versioning::DynamicVersionPolicy;
 pub use versioning::VersionPolicy;