fix(lambda-http): build query strings in a deterministic order

[abhiishek340]

📬 Issue #, if available: Fixes #1181

✍️ Description of changes:

ALB, API Gateway REST (v1) and VPC Lattice requests rebuild the URI query string in build_request_uri from a QueryMap. QueryMap wraps a HashMap with a per-instance random seed, so the same event produced a differently ordered query string each time. Apps that sign, hash or compare the raw URL (CakePHP FormProtection, Laravel signed URLs, cache keys) fail intermittently. API Gateway HTTP (v2) isn't affected because it uses raw_query_string.

This PR implements option 2 from the issue: build_request_uri now serializes the pairs sorted by key. It uses the same form_urlencoded serializer that QueryMap::to_query_string uses, so escaping is unchanged. The sort is stable, so repeated keys keep their value order (b=2&b=1 stays b=2&b=1).

Sorting doesn't restore the original request order. The issue's option 1 would need an insertion-ordered map in query_map and confirmation that ALB preserves key order in its JSON, so I kept this change local to lambda-http. It makes the URI stable either way, and it matches order-independent schemes such as Laravel's, which sign with keys sorted.

Testing:

• New alb_request_query_string_order_is_deterministic test: it deserializes the issue's ALB event 64 times and asserts one exact URI. It fails on main (e.g. ?b=2&b=1&parent_id=1&a=1&type=leader_employee) and passes with this change.
• cargo test -p lambda_http --all-features: 98 unit and 6 doc tests pass.
• cargo check -p lambda_http --no-default-features --features <each of alb, apigw_rest, apigw_http, apigw_websockets, vpc_lattice>: no new warnings compared to main.

🔏 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.