fix(lambda-http): into_api_gateway_v2_request joins cookies with "; "

[sbougerel]

into_api_gateway_v2_request reconstructs the Cookie header by joining the cookies array from the API Gateway v2 event payload with ";" (no space). This violates RFC 6265 §4.2.1, which mandates "; " (semicolon followed by a space) as the cookie-pair separator. The result is a non-compliant Cookie header that breaks any downstream cookie parser that follows the spec strictly like BetterAuth.

📬 Issue #, if available:

Closes #1142

✍️ Description of changes:

The Cookie header reconstructed from into_api_gateway_v2_request now joins pairs with "; " to produce a spec-compliant value:

cookie1=value1; cookie2=value2

The corresponding test was updated.

🔏 By submitting this pull request

• I confirm that I've ran cargo +nightly fmt.
• I confirm that I've ran cargo clippy --fix.
• I confirm that I've made a best effort attempt to update all relevant documentation.
• I confirm that my contribution is made under the terms of the Apache 2.0 license.