refactor!: demote chime-validation-max-retries to private defvar

This is an internal startup-timing parameter, not a knob real users have
reason to tune through `M-x customize'. I demoted it from defcustom to
defvar and renamed it to `chime--validation-max-retries' to make the
private status explicit. Anyone who was overriding it can keep doing so
with `setq' (the variable still exists, just under the new name).

The three customize-time validation tests went away with the defcustom —
nothing left to validate at customize-time once it stops being a
customize-target. The setter helper still applies to the other five
numeric defcustoms.

Test files that referenced the variable (`test-chime-validation-retry.el',
`test-integration-chime-mode.el') were renamed mechanically along with
the source.

Breaking change: `(setq chime-validation-max-retries N)' becomes
`(setq chime--validation-max-retries N)' if you actually had it. Most
users won't have touched it.

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/test-integration-chime-mode.el b/tests/test-integration-chime-mode.el
index cd1fec5..40436fb 100644
--- a/tests/test-integration-chime-mode.el
+++ b/tests/test-integration-chime-mode.el
@@ -105,7 +105,7 @@ in the tooltip, not go blank."
         (org-agenda-files nil)
         (chime--validation-done nil)
         (chime--validation-retry-count 0)
-        (chime-validation-max-retries 0))
+        (chime--validation-max-retries 0))
     (unwind-protect
         (progn
           (chime-mode 1)