fix: initializing self.slurm_logdir (#206)

setting `self.slurm_logdir` in `post_init`, else starts without
something… to do, will encounter uninitialized `self.slurm_logdir
attribute

This PR ought to fix #198 

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Improvements**
  - Enhanced SLURM log directory management
  - Added flexibility for custom log directory configuration
  - Simplified log directory initialization process

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: cmeesters

snakemake_executor_plugin_slurm/__init__.py

@@ -122,7 +122,11 @@ def __post_init__(self):
         self._fallback_account_arg = None
         self._fallback_partition = None
         self._preemption_warning = False  # no preemption warning has been issued
-        self.slurm_logdir = None
+        self.slurm_logdir = (
+            Path(self.workflow.executor_settings.logdir)
+            if self.workflow.executor_settings.logdir
+            else Path(".snakemake/slurm_logs").resolve()
+        )
         atexit.register(self.clean_old_logs)
 
     def clean_old_logs(self) -> None:
@@ -180,12 +184,6 @@ def run_job(self, job: JobExecutorInterface):
         except AttributeError:
             wildcard_str = ""
 
-        self.slurm_logdir = (
-            Path(self.workflow.executor_settings.logdir)
-            if self.workflow.executor_settings.logdir
-            else Path(".snakemake/slurm_logs").resolve()
-        )
-
         self.slurm_logdir.mkdir(parents=True, exist_ok=True)
         slurm_logfile = self.slurm_logdir / group_or_rule / wildcard_str / "%j.log"
         slurm_logfile.parent.mkdir(parents=True, exist_ok=True)