fix: PGHOST, PGPORT dotenv

[tianzhou]

Fix #40

[Copilot]

Pull Request Overview

This PR fixes environment variable handling for PGHOST and PGPORT by consolidating dotenv functionality into PreRun functions rather than flag defaults.

• Refactored environment variable handling to use PreRun functions instead of flag defaults
• Created new PreRun function variants to handle optional connection parameters (host, port, app name)
• Added comprehensive tests for the environment variable utility functions

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
cmd/util/env.go	Added new PreRun function variants to handle host, port, and app name environment variables
cmd/util/env_test.go	Added comprehensive test coverage for environment variable utility functions
cmd/dump/dump.go	Updated to use new PreRun function and removed env defaults from flag definitions
cmd/plan/plan.go	Updated to use new PreRun function and removed env defaults from flag definitions
cmd/apply/apply.go	Updated to use new PreRun function with app name support and removed env defaults from flag definitions
cmd/dump/dump_test.go	Removed duplicate test functions that are now covered in the util package

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[Copilot]

[nitpick] Consider using a more explicit approach by creating a struct to hold the optional parameters instead of passing multiple nil values. This would make the function calls clearer and reduce the risk of passing parameters in the wrong order.