fix: parse import-url suffixes from right

[cotishq]

Description

• Fix import-url argument parsing so URLs containing : (scheme/ports/etc.) are preserved when using the optional :true|false[:secret] suffixes.
• Add unit tests covering ports, paths, query strings, fragments, and secret suffix parsing.
• Update import-url docs with the new parsing behavior and examples.
• Make context_test create its testdata/ directory before writing the test config file (stabilizes test runs).

Before:

After the fix:

Related issue(s)

Fixes #260

[cotishq]

@Harsh4902 would love your opinion on this and what changes it still requires