fix: ensure shm writers are cleared at shutdown

[K3das]

closes #55 and makes progress on #56

Description

• Adds context cancellation to decom and waits for decom channels to close before exiting gsw_service.
• Makes influx configuration optional.
• Expands the logger API to expose the underlying zap logger and improves the logging of gsw_service and the influx writer.

Tested by stopping gsw_service and ensuring no SHM descriptors are left.

[Copilot]

Pull request overview

This PR enhances the shutdown behavior of the GSW service to ensure proper cleanup of shared memory (SHM) writers. It introduces context-based cancellation to the decom subsystem and expands the logger API to expose the underlying zap logger for improved structured logging.

Key changes:

• Added context cancellation support to TelemetryPacketWriter to enable graceful shutdown
• Exposed the underlying zap logger through a new Log() function in the logger API
• Improved structured logging throughout decom and database writer components

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 7 comments.

File	Description
proc/decom.go	Refactored TelemetryPacketWriter to accept context, return errors, and use structured logging with proper UDP connection cleanup
lib/logger/logger.go	Added Log() function to expose the underlying zap logger for creating scoped loggers
cmd/gsw_service.go	Updated to use context-aware decom initialization, wait for channel closure on shutdown, and made database configuration optional
proc/db_write.go	Enhanced logging with scoped logger and structured fields for the database writer

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