blockdev: support bootloader update on MBR

[HuijingHei]

Based on updates in bootc-dev/bootc#1773

Fixes: #1019

[gemini-code-assist]

Code Review

This pull request effectively adds support for bootloader updates on MBR partitioned disks, which resolves an issue with multipath devices. The main changes are:

1. MBR Support: The get_esp_partition function in src/blockdev.rs is refactored to use find_partition_of_esp from the bootc-internal-blockdev crate. This is a great improvement as it centralizes the logic for finding ESP partitions and extends support to MBR disks, which was the primary goal.

2. Improved Command Output: Across several files (src/efi.rs, src/filetree.rs, src/grubconfigs.rs), calls to external commands like mount, umount, efibootmgr, cp, and grub2-editenv have been updated from run() to run_inherited(). This change makes the tool more transparent by showing the output of these commands, which is very helpful for debugging and user feedback.

The changes are clean, focused, and correctly implemented. The code quality is excellent. I have no issues to report.