Fix Any recursion depth for packed regular messages

[XananasX7]

This updates Python ProtoJSON parsing so regular messages packed inside Any are routed through ConvertMessage() instead of directly through _ConvertFieldValuePair().

ConvertMessage() owns max_recursion_depth accounting. The existing nested-Any fix already uses it for well-known types, but the regular-message branch still bypassed one message-entry depth step. That
allowed alternating Any -> regular message -> Any -> regular message inputs to consume less recursion budget than equivalent nested messages.

The patch also restores the recursion-depth counter with finally, so failed parses do not leave stale parser state.

A regression test covers:

• deeply nested Any values packing proto3.TestAny, which now fail at max_recursion_depth=5
• a shallower packed regular-message chain that still parses successfully

Validation:

• python3 -m py_compile python/google/protobuf/json_format.py python/google/protobuf/internal/json_format_test.py
• git diff --check origin/main..HEAD
• local dynamic-descriptor harness confirming 2 packed regular wrappers pass at depth 5 and 3 wrappers fail