Fix URI encoding to preserve RFC 3986 unreserved characters in Aliyun signature

[Copilot]

The Aliyun signature module was incorrectly percent-encoding RFC 3986 unreserved characters (-, _, ., ~) in URI paths and query strings, causing signature mismatches with the Aliyun API.

Changes

• Created UNRESERVED encoding set by removing unreserved characters from NON_ALPHANUMERIC per RFC 3986
• Updated canonicalize_uri() to preserve -_.~ in path segments
• Updated build_canonical_query_string() to preserve -_.~ in query keys and values
• Added tests validating unreserved character preservation and path separator handling

Example

Before:

// Using NON_ALPHANUMERIC encoded everything except alphanumerics
"key-1" → "key%2D1"
"value_2" → "value%5F2"  
"/path.with~chars" → "/path%2Ewith%7Echars"

After:

// Using UNRESERVED preserves RFC 3986 unreserved characters
"key-1" → "key-1"
"value_2" → "value_2"
"/path.with~chars" → "/path.with~chars"

Implementation

The UNRESERVED encoding set is created by removing the four unreserved punctuation marks from NON_ALPHANUMERIC:

const UNRESERVED: &AsciiSet = &NON_ALPHANUMERIC
    .remove(b'-')
    .remove(b'_')
    .remove(b'.')
    .remove(b'~');

Path separators (/) are preserved by splitting before encoding segments.

Original prompt

https://github.com/daflyinbed/janus/blob/aliyun/src/aliyun/signature.rs 里面 canonicalize_uri和build_canonical_query_string里面序列化的时候 字符-、_、.、~也不应该编码

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[daflyinbed]

@copilot 不对 直接在NON_ALPHANUMERIC上add我提到的几个要无视的字符

[Copilot]

@copilot 不对 直接在NON_ALPHANUMERIC上add我提到的几个要无视的字符

Done! Changed to use NON_ALPHANUMERIC.remove() for -, _, ., ~ characters in commit 8a14c91.