Standardize LSN formatting by zero padding

Standardize LSN formatting by zero padding

This commit standardizes the output format for LSNs to ensure consistent
representation across various tools and messages.  Previously, LSNs were
inconsistently printed as `%X/%X` in some contexts, while others used
zero-padding.  This often led to confusion when comparing.

To address this, the LSN format is now uniformly set to `%X/%08X`,
ensuring the lower 32-bit part is always zero-padded to eight
hexadecimal digits.

Author: Japin Li <japinli@hotmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Discussion: https://postgr.es/m/ME0P300MB0445CA53CA0E4B8C1879AF84B641A@ME0P300MB0445.AUSP300.PROD.OUTLOOK.COM