fix(dendrite): skip axon on is_validator RPC failure instead of silently including (#168)

[RUNECTZ33]

Summary

Closes #168.

dendrite_lite.discover_validators (allways/cli/dendrite_lite.py:60-66) wraps contract_client.is_validator(...) in try / except Exception: pass. The pass falls through to axons.append(axon), so any RPC failure during validator-permit checking silently includes the unverified hotkey in the CLI broadcast list. Issue #73 / PR #92 already addressed the same pattern on the validator-side dendrite — CLI parity here.

Change

-            except Exception:
-                pass
+            except Exception as e:
+                bt.logging.debug(
+                    f'Skipping uid={uid} hotkey={metagraph.hotkeys[uid][:12]}...: '
+                    f'is_validator RPC failed: {e}'
+                )
+                continue

Bind the exception, log a debug message naming the uid + hotkey prefix + RPC error, and continue. Matches the existing continue branches above for not validator_permit and not is_serving.

Why this is safe

• The function's contract is "return the validator-permit-AND-is-validator-confirmed list." Silently including hotkeys that weren't confirmed violates that contract.
• The CLI swap flow downstream of discover_validators rejects responses from non-validators — surfacing via confusing rejection rather than quietly skipping that hotkey upstream. Better to drop early.
• Debug-level log preserves diagnostic info for operators running with --logging.debug without polluting the normal CLI experience.

Scope

allways/cli/dendrite_lite.py: +11 / -2. No new imports (bt.logging already imported).

Test plan

• AST parses cleanly: python3 -c "import ast; ast.parse(open('allways/cli/dendrite_lite.py').read())"
• Behavior matches PR fix: skip axon when is_validator RPC fails in discover_validators #92's validator-side fix pattern (skip-on-RPC-fail, log, continue).
• Confirmed bt.logging is imported at top of file (line 5).