instead of concatenating strings, let's format using the builtin
support of `log::debug()`. for two reasons:
1. better performance, after this change, we don't need to
materialize the concatenated string, if the "debug" level logging
is not enabled. seasetar::log only formats when a certain log
level is enabled.
2. better readability. with the format string, it is clear what
is the fixed part, and which arguments are to be formatted.
this also helps us to move to compile-time formatting check,
as fmtlib requires the caller to be explicit when it wants
to use runtime format string.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#14627
25f4a7c400