nanobsd: Change sizes to use bytes exclusively

[senguptaangshuman17_gmail.com]

Summary

Accept sizes in bytes instead of 512-byte sectors. Replace strsuftoll with strtobytes, which accepts powers of two and powers of ten.

For existing configurations migrating to the default plan, users who wish to keep using 512-byte sector counts can append an 's' (for sector) suffix to their variables (e.g., NANO_MEDIASIZE=4000000s, NANO_CONFSIZE=2048s).

Legacy configurations setting NANO_PLAN=legacy continue working with raw sector counts without modification.

[senguptaangshuman17_gmail.com]

Rebase stack on top of D59043 update

[jlduran]

Since this is a legacy-breaking change (perhaps the most significant one), we should provide an easy migration path. For example, in the commit message, we can explain that users who want to keep using sector sizes could add an s (for sector) suffix to its current values when migrating to the default plan, this is a deliberate change from strsuftoll, which uses b (for block) for that same purpose.

tools/tools/nanobsd/defaults.sh

1486

This change seems unrelated.

[senguptaangshuman17_gmail.com]

Add metalog file existence check before makefs and calculate md_size in sectors