mdbx++: rework buffer::silo to avoid use std::string.

.github/actions/spelling/expect.txt

@@ -9,6 +9,7 @@ acision
 AClass
 adata
 addprefix
+addressof
 addsuffix
 addtogroup
 advapi
@@ -104,6 +105,7 @@ bitfield
 bitmaps
 bitmask
 bitness
+bitops
 blogger
 blogs
 blogspot
@@ -171,6 +173,7 @@ cifs
 cinttypes
 circleci
 claude
+climits
 clockid
 CLOEXEC
 closefile
@@ -787,6 +790,7 @@ kval
 Lanfranchi
 largedata
 largepage
+lastbyte
 lastest
 lastvalue
 lastword
@@ -1650,6 +1654,7 @@ svg
 svnweb
 svr
 swait
+swappable
 symas
 SYMLINKS
 syncbytes