Add logging abstraction layer for glog deprecation

[yurekami]

Summary

• Introduces include/util/logging.h that provides glog-compatible macros (LOG, VLOG, CHECK, DCHECK, CHECK_NOTNULL) with a lightweight fallback implementation
• This enables gradual migration away from glog dependency
• When USE_GLOG is defined: uses glog as before
• Otherwise: uses minimal stderr-based logging with UCCL_VLOG_LEVEL env var for verbose level control

Updated key headers to use the new abstraction:

• include/util/util.h
• include/util/timer.h
• include/util/net.h
• include/util/shared_pool.h

Test plan

• Build with USE_GLOG defined - should use glog as before
• Build without USE_GLOG - should use lightweight fallback
• Verify UCCL_VLOG_LEVEL environment variable controls verbose logging

Addresses #295

🤖 Generated with Claude Code

[YangZhou1997]

Hi @yurekami , thank you for the contribution! We actually have some plans on this and would like a similar interface to NCCL's one: https://github.com/NVIDIA/nccl/blob/master/src/debug.cc. Would you like to convert to NCCL's APIs and implementation?

[yurekami]

Thanks for the pointer to NCCL's debug.cc! I'll study that implementation and revise this PR to align with NCCL's logging interface. This would provide better consistency for users familiar with NCCL debugging.

[yurekami]

Thanks for the feedback @YangZhou1997! I've revised the implementation to use NCCL-style logging API.

Changes

include/util/logging.h now provides:

• ncclDebugLogger_t function pointer storage (set via uccl::logging::initLogger())
• NCCL-style macros matching the interface from NCCL's debug.cc:
  • INFO(flags, fmt, ...) - info-level logging with subsystem flags
  • WARN(fmt, ...) - warning-level logging
  • TRACE(flags, fmt, ...) - trace-level logging
• Subsystem flags: UCCL_INIT, UCCL_NET, UCCL_P2P, UCCL_ALL
• Fallback stderr logger when NCCL logger is unavailable

collective/rdma/nccl_plugin.cc updated as reference:

ncclResult_t pluginInit(ncclDebugLogger_t logFunction) {
  uccl::logging::initLogger(logFunction);
  INFO(UCCL_INIT, "UCCL RDMA plugin initialized, PID: %d", getpid());
  ...
}

The EFA and afxdp plugins can be migrated similarly in follow-up PRs.