feat: add feature-gated tracing/logging infrastructure

[tmthecoder]

Summary

Replace all println! calls with structured tracing macros and add a feature-gated logging infrastructure that library consumers can opt into without being burdened by unnecessary dependencies.

Changes

Infrastructure

• smb-core/src/logging.rs — New module with feature-gated macro wrappers. When tracing is enabled, re-exports tracing::{trace, debug, info, warn, error, info_span, debug_span, trace_span}. When disabled, all macros compile to no-ops.
• smb-core/Cargo.toml — Added tracing as optional dependency with tracing and logging features.
• smb/Cargo.toml — Added tracing and tracing-subscriber as optional dependencies. Features are fully independent and opt-in.

Features (all opt-in, none forced by server)

Feature	What it enables
server	Async runtime (tokio, tokio-stream, tokio-util) — no tracing
tracing	Structured tracing via tracing crate + tracing-subscriber
logging	Everything in tracing + log crate compatibility bridge

Log level conventions

Level	Usage
error!	Unrecoverable failures, unexpected states
warn!	Recoverable issues, parse failures handled gracefully
info!	Lifecycle events: server start, connection accepted, session setup complete
debug!	Operational detail: command dispatch, handler delegation, message send/receive
trace!	Sensitive data only: keys, signatures, raw buffers, NTLM flags, full message dumps

Files modified (26 files, 331 insertions, 95 deletions)

New:

• smb-core/src/logging.rs

println! → tracing (18 files):

• smb/src/server/connection.rs, session.rs, mod.rs, message_handler.rs, tree_connect.rs, share/file_system.rs
• smb/src/socket/message_stream/mod.rs, stream_async.rs
• smb/src/protocol/message.rs, body/negotiate/context.rs, body/create/request_context.rs, body/create/response_context.rs, body/tree_connect/buffer.rs
• smb/src/util/auth/spnego/der_utils.rs, spnego_token.rs, spnego_token_response.rs
• smb/src/util/auth/ntlm/ntlm_authenticate_message.rs
• smb/src/main.rs — subscriber init behind #[cfg(feature = "tracing")], defaults to RUST_LOG=info

Commented-out println! cleanup (4 files):

• smb-core/src/lib.rs, smb-derive/src/attrs.rs, field.rs, field_mapping.rs

Verification

• cargo check -p smb-core ✅
• cargo check -p smb-core --features tracing ✅
• cargo check -p smb-derive ✅
• cargo check -p smb_reader --features server ✅ (no tracing)
• cargo check -p smb_reader --features "server,tracing" ✅
• cargo check --bin spin_server_up --features "server,tracing,anyhow" ✅
• grep -r println! */src/ — zero results