simplify Level type and align with slog.Level

[rashmi-tondare]

This PR addresses issue #738

Changes

• Type alias refactoring: Changed Level type from a custom independent type to an alias of slog.Level in interceptors/logging/slog.go
• Simplified documentation: Updated comments in slog.go to reflect that Level is now an alias, removing the inherited documentation about level numbering constraints (which now belong to slog)

Benefits

• Better alignment with Go's standard library
• Reduced code duplication
• Seamless interoperability between go-grpc-middleware logging and standard slog
• Non-breaking change for users of the library

Verification

• Confirmed the Level alias maintains the same API surface as the previous implementation
• All existing constants (LevelDebug, LevelInfo, LevelWarn, LevelError) continue to work identically
• No changes required to the Logger interface or existing middleware implementations
• Verified by checking usage in LoggerFunc, DefaultClientCodeToLevel, and internal test code — all continue to work as expected

[rashmi-tondare]

The linting workflow fails because it's unable to access the Medium link in the readme (see logs here). The link is accessible but looks like Medium blocks this automated check.

Is there a way to fix or skip this check?

[johanbrandhorst]

One question, this looks great.

[johanbrandhorst]

Do we need this?

[rashmi-tondare]

The only purpose of adding this was so that the documentation comment for the Logger interface renders the hyperlink to the slog.Level implementation.
It is non-essential and I can remove it if not required.

[johanbrandhorst]

Huh, TIL

[johanbrandhorst]

The linting workflow fails because it's unable to access the Medium link in the readme (see logs here). The link is accessible but looks like Medium blocks this automated check.

Is there a way to fix or skip this check?

Sorry about that, we can just ignore that failure.