Fix: Add support for Base64 strings without padding (Issue #2501)

[jamro]

fix(isBase64): Add support for Base64 strings without padding (Issue #2501)

• Updated isBase64 function to handle Base64 strings with missing padding.
• Includes tests for both padded and unpadded Base64 strings.
• Introduced a config option to toggle padding handling behaviour (ignorePadding).

Fix: #2501

Reference: Base64 RFC

3.2 Padding of Encoded Data
   In some circumstances, the use of padding ("=") in base-encoded data
   is not required or used.

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)
• References provided in PR (where applicable)