fix(ext/node): CBC decipher setAutoPadding(false) incorrectly strips bytes (#32403)
## Summary
- `Decipheriv.final()` unconditionally stripped PKCS7 padding from
decrypted output regardless of the `#autoPadding` flag, corrupting data
when `setAutoPadding(false)` was used
- Made the PKCS7 padding stripping conditional on `this.#autoPadding`
- Added tests for `aes-256-cbc` and `aes-128-cbc` roundtrips with
`setAutoPadding(false)`
Closes #28381
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>