fix(parser): recognize options after rest positional items

[takeokunn]

Why

A :rest-p positional took every remaining token, so options written after its first item were collected as positionals. search foo src --output count produced paths ("src" "--output" "count"). docs/src/guide/cli-behavior.md ("Interspersed arguments") already promised that command and global options may follow positionals. A consumer (aitools) had to replace its rest positional with 16 optional positionals to work around it.

What to review

• src/parser-cps.lisp: the mixed-argument scanner takes rest items one token at a time and keeps checking later tokens as options until a literal --. The rest spec is applied once when the tokens run out, so :min-count/:max-count, value parsing and defaults behave as before. Only internal % functions changed arity.
• Behavior change for consumers: a CLI that relied on a rest positional swallowing option-looking tokens (for example nshell build.ns --json) now gets cli-unknown-option and needs -- or a :stop-parsing-p option. docs/src/guide/migration-guide.md notes this for nshell. Downstream CLIs were not checked.
• Error ordering: rest items are parsed and count-checked at the end of the scan instead of at the first rest token.

Verification outside CI

t/parser-cps-rest-positional-test.lisp (15 tests) covers long options in both spellings, flags, short clusters, global options after the subcommand, -- (including a second --), negative numbers allowed and rejected, zero rest items, min/max counts across split items, unknown options, --help, bare -, and a root-level rest positional. Against the unfixed parser, 13 of them failed.

A consumer executable (aitools, asdf:program-op) builds against this commit, loading cl-cli starts no threads, and aitools replace x y a.txt --expect-count 4 now reads the option after the path.

Release

main already declares 1.4.0 (asd, demo, README pin) from unreleased feature commits (define-option, define-positional, the cl-cli/concurrent system), and v1.4.0 was never tagged. This fix ships in that release.