Apply endianness override if spec was provided (#191)

* apply endianness override if spec is provided

* Fix endianness determination logic

Updated the logic for determining endianness to correctly prioritize user settings. This ensures the inferred endianness is only used if both the provided specification and user settings do not specify it.

---------

Co-authored-by: Altay Sansal <altay.sansal@tgs.com>

src/segy/file.py

@@ -134,6 +134,7 @@ def __init__(
         self._info = self.fs.info(self.url)
 
         # Spec setting overrides.
+        # The control flow here is terrible; needs a refactor.
         if self.settings.binary.revision is not None:
             self.spec = get_segy_standard(self.settings.binary.revision)
 
@@ -151,9 +152,14 @@ def __init__(
         # If spec is provided set to it and update endianness if its None.
         else:
             self.spec = spec
+
+            # Override/Infer endianness
             if self.spec.endianness is None:
-                scan_result = infer_endianness(self.fs, self.url, self.spec)
-                self.spec.endianness = scan_result.endianness
+                if self.settings.endianness is None:
+                    scan_result = infer_endianness(self.fs, self.url, self.spec)
+                    self.spec.endianness = scan_result.endianness
+                else:
+                    self.spec.endianness = self.settings.endianness
 
         self._update_spec()
         self.accessors = TraceAccessor(self.spec.trace)