Fix issue #3,if format not i18n key will return format self - #4

Fix #3 Currently, the Tr() function in this package assumes that any string containing a dot (.) is an i18n key in the format section.key. This causes unexpected behavior when passing normal user-facing strings such as:

i18n.Tr("en-US", "Go 1.20 project")

Instead of returning the original string "Go 1.20 project", it incorrectly splits the string and tries to resolve "1" as a section and "20 project" as a key, ultimately returning "20 project" or an unexpected fallback.

Fix
This PR modifies the Tr() function so that:

1. If no translation is found using the section.key approach, it gracefully falls back to returning the original input string (format).
2. It maintains full backward compatibility with existing section.key style lookups.
3. It preserves support for optional parameters (args) passed to Tr() using fmt.Sprintf.

Example Behavior (After Fix)

i18n.Tr("en-US", "Go 1.20 project") // ➜ returns "Go 1.20 project"
i18n.Tr("en-US", "site.title")      // ➜ returns value from i18n messages if defined