feat: add solutions for lc No.1915

[yanglbme]

No description provided.

[Copilot]

Pull request overview

Adds/updates LeetCode 1915 (“Number of Wonderful Substrings”) solutions, including a new Rust implementation, and aligns the Python implementation/snippets with the same prefix-xor counting approach.

Changes:

• Added a Rust solution using prefix parity bitmask counting.
• Updated the Python solution (and README snippets) to use defaultdict(int) and a summed lookup across the 10 toggled states.
• Expanded the English README with a clearer algorithm explanation and added the Rust snippet to both READMEs.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
solution/1900-1999/1915.Number of Wonderful Substrings/Solution.rs	New Rust solution implementing prefix XOR + counting over 10-bit states.
solution/1900-1999/1915.Number of Wonderful Substrings/Solution.py	Python solution updated to defaultdict(int) and a compact summed contribution for 1-bit toggles.
solution/1900-1999/1915.Number of Wonderful Substrings/README.md	Updates Python snippet accordingly and adds a Rust snippet section.
solution/1900-1999/1915.Number of Wonderful Substrings/README_EN.md	Adds detailed explanation title/text, updates Python snippet, and adds Rust snippet section.

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