Update Slogs logger to handle AddSource

[Starttoaster]

AddSource, when enabled on a slog logger, adds context to a log about the location in the code of the caller. This can help with debugging in circumstances where multiple pieces of code may have similar message data. See an example below:

time=2026-01-26T16:27:54.487-08:00 level=ERROR source=/path/in/program/main.go:25 msg="loading config" error="CLOUDFLARE_API_TOKEN environment variable is required"

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Note

Medium Risk
Changes the logging API (Init signature) and rewires log emission, which may break existing callers and subtly affect log formatting/source attribution if the new record construction is incorrect.

Overview
Updates pkg/slogs to support configurable handler behavior via options: Init now accepts functional options (e.g., WithSourceContext to emit correct caller locations and WithWriter to redirect output) and the logger is reworked to build slog.Records manually so AddSource points at the real caller.

Adds level-specific and context-aware logging methods (Debug/Info/Warn/Error/Fatal plus *Context variants) with internal error handling, and updates the README with the new initialization options and examples.

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