Problem: forge tokens were visible as raw text with no virtual text
labels, and the eol separator logic collapsed all gaps when
non-adjacent specifiers were absent.
Solution: add forge conceal syntax patterns in `setup_syntax()`, add
`PendingForge`/`PendingForgeClosed` highlight groups, handle the
`%l` specifier in `build_eol_virt()`, fix separator collapsing to
buffer one separator between present segments, and change
`concealcursor` to `nc` (reveal in visual and insert mode).
Barrett Ruth
f4e62b148c