Fix mysql dialect text docstring, length is interpreted as byte size

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### Description
The `Text` and its variant types in MySQL are bytes size limited, not character length, so fixing the doctoring where the upper limit uses the `characters` as the unit instead of `bytes`

https://dev.mysql.com/doc/refman/5.7/en/storage-requirements.html
https://dev.mysql.com/doc/refman/8.0/en/storage-requirements.html

<img width="878" alt="Screenshot 2024-02-15 at 17 27 59" src="https://github.com/sqlalchemy/sqlalchemy/assets/5219229/29731769-f57e-46f9-858b-46feda0ae83c">

### Checklist
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This pull request is:

- [x] A documentation / typographical / small typing error fix
	- Good to go, no issue or tests are needed
- [ ] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #11018
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/11018
Pull-request-sha: 13fa52917efea9a229c7abf19a3be40e24a79cb9

Change-Id: Iea903a6dc4b52ee4b7b5d2d64256c69abbd1f8aa
(cherry picked from commit 1c58fe53b6fd069cbb82955ddaf9eb5405076146)
(cherry picked from commit 51011db22b0d51b5560d55b97671631cadc10265)

diff --git a/lib/sqlalchemy/dialects/mysql/types.py b/lib/sqlalchemy/dialects/mysql/types.py
index a8a6042f897c197adf3a61b9190ff770f0354660..a7996189b76e247e311a7d37cda942628884fb4b 100644 (file)
--- a/lib/sqlalchemy/dialects/mysql/types.py
+++ b/lib/sqlalchemy/dialects/mysql/types.py
@@ -499,7 +499,7 @@ class YEAR(sqltypes.TypeEngine):
 
 
 class TEXT(_StringType, sqltypes.TEXT):
-    """MySQL TEXT type, for text up to 2^16 characters."""
+    """MySQL TEXT type, for character storage encoded up to 2^16 bytes."""
 
     __visit_name__ = "TEXT"
 
@@ -508,7 +508,7 @@ class TEXT(_StringType, sqltypes.TEXT):
 
         :param length: Optional, if provided the server may optimize storage
           by substituting the smallest TEXT type sufficient to store
-          ``length`` characters.
+          ``length`` bytes of characters.
 
         :param charset: Optional, a column-level character set for this string
           value.  Takes precedence to 'ascii' or 'unicode' short-hand.
@@ -535,7 +535,7 @@ class TEXT(_StringType, sqltypes.TEXT):
 
 
 class TINYTEXT(_StringType):
-    """MySQL TINYTEXT type, for text up to 2^8 characters."""
+    """MySQL TINYTEXT type, for character storage encoded up to 2^8 bytes."""
 
     __visit_name__ = "TINYTEXT"
 
@@ -567,7 +567,8 @@ class TINYTEXT(_StringType):
 
 
 class MEDIUMTEXT(_StringType):
-    """MySQL MEDIUMTEXT type, for text up to 2^24 characters."""
+    """MySQL MEDIUMTEXT type, for character storage encoded up
+    to 2^24 bytes."""
 
     __visit_name__ = "MEDIUMTEXT"
 
@@ -599,7 +600,7 @@ class MEDIUMTEXT(_StringType):
 
 
 class LONGTEXT(_StringType):
-    """MySQL LONGTEXT type, for text up to 2^32 characters."""
+    """MySQL LONGTEXT type, for character storage encoded up to 2^32 bytes."""
 
     __visit_name__ = "LONGTEXT"
 
@@ -683,7 +684,7 @@ class CHAR(_StringType, sqltypes.CHAR):
         super(CHAR, self).__init__(length=length, **kwargs)
 
     @classmethod
-    def _adapt_string_for_cast(self, type_):
+    def _adapt_string_for_cast(cls, type_):
         # copy the given string type into a CHAR
         # for the purposes of rendering a CAST expression
         type_ = sqltypes.to_instance(type_)