add zig codes for Section Binary Tree, Binary Search Tree and AVL Tree

[codingonion]

If this PR is related to coding or code translation, please fill out the checklist.

• [x] I've tested the code and ensured the outputs are the same as the outputs of reference codes.
• [x] I've checked the codes (formatting, comments, indentation, file header, etc) carefully.
• [x] The code does not rely on a particular environment or IDE and can be executed on a standard system (Win, macOS, Ubuntu).

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1 Ignored Deployment

Name	Status	Preview	Comments	Updated
hello-algo	⬜️ Ignored (Inspect)			Jan 22, 2023 at 6:54AM (UTC)

[codingonion]

The output of "codes/zig/chapter_tree/binary_tree_dfs.zig" is shown below,

The output of "codes/zig/chapter_tree/binary_search_tree.zig" is shown below,

The output of "codes/zig/chapter_tree/avl_tree.zig" is shown below,