Build: Correct LICENSE paths for wheels and document the bundled Cython runtime (#3893)

* Build: Correct LICENSE paths for wheels and document the bundled Cython runtime

The wheel ships fb303 and hive_metastore as top-level packages (setup.py package_dir), so the LICENSE entries pointing at vendor/ were wrong in binary distributions, and the compiled decoder_fast module embeds Cython runtime code that was not documented. Reword both vendored entries to describe each layout and add a Cython entry, raised in the 0.12.0 release vote thread.

Generated-by: Claude Code (Fable 5)
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Build: Cite Cython's COPYING.txt instead of an invented copyright line

Cython's LICENSE.txt carries no copyright holder line, so drop the one this
entry made up and instead record why the bundled runtime needs no NOTICE
change, as requested in review.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SQc71d6jDK1U3i4mP9os5i

* Build: Clarify generated code license entries

Describe the generated Thrift bindings using their actual sdist and wheel layouts, and align the Cython note with its licensing clarification.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Build: Describe generated fb303 code precisely

Avoid implying that the fb303 Thrift definition itself is included in source or binary distributions.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Kevin Liu <kevin.jq.liu@gmail.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: 4 people

LICENSE

@@ -216,7 +216,9 @@ License: https://www.apache.org/licenses/LICENSE-2.0
 
 This product includes code from Apache Thrift.
 
-* Uses the fb303.thrift file that's part of Hive's thrift service in vendor/fb303/
+* Includes the generated Python client and type definitions for the fb303
+  service. In source distributions, this code is located in vendor/fb303/; in
+  binary distributions, it is shipped as the top-level fb303 package.
 
 Copyright: 2006-2022 The Apache Software Foundation.
 Home page: https://thrift.apache.org/
@@ -226,10 +228,25 @@ License: https://www.apache.org/licenses/LICENSE-2.0
 
 This product includes code from Apache Hive.
 
-* Uses hive_metastore.thrift to generate the Hive Metastore client in vendor/hive_metastore/
+* Includes the Hive Metastore client generated from hive_metastore.thrift. The
+  generated code is located in vendor/hive_metastore/ in source distributions
+  and shipped as the top-level hive_metastore package in binary distributions.
 
 Copyright: 2008-2022 The Apache Software Foundation.
 Home page: https://hive.apache.org/
 License: https://www.apache.org/licenses/LICENSE-2.0
 
 --------------------------------------------------------------------------------
+
+Official binary distributions contain the pyiceberg.avro.decoder_fast
+extension, built from C code generated by Cython.
+
+* Cython generates this C code from pyiceberg/avro/decoder_fast.pyx. Cython
+  states that compilation may embed snippets in generated output, but that the
+  output is not a derivative work of Cython and those snippets impose no
+  license restrictions.
+
+Cython licensing clarification:
+https://github.com/cython/cython/blob/2f3a781dcca092ce95fbfef2736b12b0d1ab50dd/COPYING.txt
+
+--------------------------------------------------------------------------------