refactor: Simplify derive macro implementation

[0xvasanth]

Summary

• Simplify Gonfig derive macro code generation
• Fix remaining clippy warnings in core library files

Changes

Code Simplification

• Extract shared logic: Created reusable setup_env_cli code block to eliminate duplication between from_gonfig_with_builder() and gonfig_builder() methods
• Simplify config file loading: Replaced verbose if-else chain with clean loop over config file types
• Clean up variable usage: Removed unused allow_env variable
• Streamline environment key generation: Simplified logic with cleaner pattern matching
• Remove redundant comments: Cleaned up unnecessary code comments

Code Quality

• Fixed clippy::uninlined_format_args warnings in core library:
  • src/builder.rs
  • src/cli.rs
  • src/config.rs

Benefits

1. Reduced code duplication: Shared environment/CLI setup logic now in one place
2. Better maintainability: Future changes only need to be made once
3. Improved readability: Cleaner, more concise code flow
4. Consistent style: All format strings follow modern Rust conventions

Test plan

• All existing tests pass
• Clippy passes with -D warnings
• No functional changes, only refactoring

[Copilot]

Pull Request Overview

Refactor to simplify the derive macro implementation and address remaining clippy warnings; this PR also bumps crate versions to 0.1.6 to reflect the changes.

• Bump gonfig and gonfig_derive crate versions to 0.1.6
• Align published versions across crates

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
gonfig_derive/Cargo.toml	Bump derive crate version to 0.1.6
Cargo.toml	Bump main crate version to 0.1.6

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