Add type checking for encoder/decoder parameters in latex_encoding.py

Add explicit type validation for the `encoder` and `decoder` parameters
in LatexEncodingMiddleware and LatexDecodingMiddleware respectively.
This provides a clear error message at initialization time rather than
a confusing AttributeError later during usage.

Also fixed missing spaces in error message strings.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: MiWeiss

bibtexparser/middlewares/latex_encoding.py

@@ -102,10 +102,15 @@ def __init__(
 
         if encoder is not None and (keep_math is not None or enclose_urls is not None):
             raise ValueError(
-                "Cannot specify both encoder and keep_math or enclose_urls."
+                "Cannot specify both encoder and keep_math or enclose_urls. "
                 "If you want to use a custom encoder, you have to specify it completely."
             )
 
+        if encoder is not None and not isinstance(encoder, UnicodeToLatexEncoder):
+            raise TypeError(
+                f"encoder must be a UnicodeToLatexEncoder instance, got {type(encoder).__name__}"
+            )
+
         # Defaults (not specified as defaults in args,
         #   to make sure we can identify if they were specified)
         keep_math = keep_math if keep_math is not None else True
@@ -167,11 +172,16 @@ def __init__(
         if decoder is not None and (keep_braced_groups is not None or keep_math_mode is not None):
             raise ValueError(
                 "Cannot specify both decoder and one of "
-                "`keep_braced_groups` or `keep_math_mode`."
+                "`keep_braced_groups` or `keep_math_mode`. "
                 "If you want to use a custom decoder, "
                 "you have to specify it completely."
             )
 
+        if decoder is not None and not isinstance(decoder, LatexNodes2Text):
+            raise TypeError(
+                f"decoder must be a LatexNodes2Text instance, got {type(decoder).__name__}"
+            )
+
         # Defaults (not specified as defaults in args,
         #   to make sure we can identify if they were specified)
         keep_braced_groups = keep_braced_groups if keep_braced_groups is not None else False