feat(cmd/gno): allow gno test to default to the current directory

[Nemanya8]

This PR resolves #3420 by enhancing the gno test command.
The command now assumes the current directory (.) as the default path when no directory is specified, aligning its behavior with go test.

Changes to CI:

• Removed the no_args test.
• Added new tests to cover the following scenarios:
  • Valid test execution.
  • Valid file-based test.
  • Test with flags.
  • Empty directory.
  • Empty test file.

This PR is a repost of #3429 with a cleaner commit history.

CC @notJoon @moul

[Gno2D2]

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[notJoon]

LGTM 👍

remove: review/triage flag