Add relevant build metadata to vdb that portage has

[ferringb]

This is related to restoring VDB metadata parity between pkgcore and portage for a collection of attributes.

• BUILD_TIME is trivial, and should be threaded through the built object interface. Portage stores int(time.time()) for this.
• FEATURES; it's as it sounds, env["FEATURES"]
• REQUIRES: diffball for example, is x86_64: libbz2.so.1 libc.so.6 liblzma.so.5 libm.so.6 libz.so.1
• BINPKGMD5: presumably, the md5 of whatever binpkg was involved.
• SIZE: Appears to be a byte count of the pkg contents on disk. Note that the value in VDB doesn't seem to actually match the byte count on disk- it's off by a few bytes. Likely need to investigate if that value is last minute calculated, or if it is taken prior to things like debugsplit being invoked.

[ferringb]

Less sensical values, but ones that apparently now exist:

• CATEGORY
• PF (this is literally $PF)
• DEBUGBUILD (unclear what the purpose is)

[ferringb]

most recent list as of 2022-12-21:

ferringb@frith ~ $ diff -u <(ls -1 diffball-pkgcore/) <(ls -1 diffball-portage/)
--- /dev/fd/63	2022-12-21 22:44:19.851506691 -0800
+++ /dev/fd/62	2022-12-21 22:44:19.853506697 -0800
@@ -1,18 +1,21 @@
 BDEPEND
+BINPKGMD5
+BUILD_TIME
+CATEGORY
 CBUILD
 CFLAGS
 CHOST
 CONTENTS
 COUNTER
-CTARGET
 CXXFLAGS
+DEBUGBUILD
 DEFINED_PHASES
 DEPEND
 DESCRIPTION
 diffball-1.0.1-r2.ebuild
-DISTFILES
 EAPI
 environment.bz2
+FEATURES
 HOMEPAGE
 INHERITED
 IUSE
@@ -22,12 +25,12 @@
 LICENSE
 NEEDED
 NEEDED.ELF.2
-PDEPEND
-PKGMANAGER
-PROPERTIES
+PF
+PROVIDES
 RDEPEND
 repository
+REQUIRES
 RESTRICT
+SIZE
 SLOT
 USE
-USER_PATCHES