LANG-1806: Allow floating-point suffixes in NumberUtils.isParsable

[Jagdish-Singh-Bisht]

This PR addresses LANG-1806 as a small follow-up to LANG-1695.

NumberUtils.isParsable currently rejects strings such as "1.f" and "1.d", even though Float.parseFloat("1.f") and Double.parseDouble(1.d") succeed.

The test suite already contained TODOs for these cases, this change uncomments those assertions and updates the parsing logic to allow floating-point suffixes (f/F/d/D) only when they appear as the final character.

The change is intentionally minimal and doesn not affect other numeric formats.

[garydgregory]

Hello @Jagdish-Singh-Bisht

This PR doesn't handle:

• 1.2e-5d
• 1.2e-5f

You did not follow the instructions in the PR template:

• Run mvn
• Fix all errors
• Also remove the extra blank lines.

Rebase on git master where I added test TODOs for the above.

[Jagdish-Singh-Bisht]

Thanks for the review.

Understood regarding the scientific notation cases (1.2e-5d / 1.2e-5f).
I'll rebase on current master, address those cases, clean-up formatting, and confirm mvn test before updating the PR.