v1.0.0: extract theme from cl-tty.box to own cl-tty.theme package

The theme system (theme class, define-preset, load-preset, theme-color)
was part of the bloated cl-tty.box package even though it had nothing
to do with boxes, spans, or component rendering. It only used cl-tty.backend
for the *theme-colors* hash table.

Changes:
- added defpackage :cl-tty.theme as the first block in theme.lisp
  (inline defpackage avoids ASDF dependency ordering issues with
   separate package files)
- removed theme exports from cl-tty.box defpackage
- theme tests now run in their own THEME-SUITE (16 tests) instead of
  part of BOX-SUITE
- box suite drops from 64 to 48 tests (16 moved to theme suite)
- updated ASDF, run-all-tests.lisp

All 15 test suites pass at 100%.

run-all-tests.lisp

@@ -27,6 +27,7 @@
                    (:cl-tty-scrollbox-test "SCROLLBOX-SUITE")
                     (:cl-tty-markdown-test  :cl-tty-markdown-test)
                     (:cl-tty-dialog-test    "DIALOG-SUITE")
+                    (:cl-tty-theme-test     "THEME-SUITE")
                     (:cl-tty-slot-test      "SLOT-SUITE")
                    (:cl-tty-layout-test    "LAYOUT-SUITE")
                    (:cl-tty-modern-backend-test "MODERN-BACKEND-SUITE")