fix: fallback to cjson after simdjson decode errors

[nic-6443]

Description

When apisix.request_body_json_lib is set to simdjson, request body decoding now logs a warning and retries with cjson if simdjson returns a decode error. This keeps simdjson as the default fast path while preserving the existing cjson behavior as a fallback path.

This also updates api7-lua-resty-simdjson to 0.1.2-1, which includes decoder state cleanup after errors.

Checklist

• Tests added
• Documentation updated

Tests

• TEST_NGINX_CASE=19 prove -Itest-nginx/lib -I. -r t/core/request.t
• prove -Itest-nginx/lib -I. -r t/core/request.t
• prove -Itest-nginx/lib -I. -r t/plugin/ai-proxy-simdjson-error-state.t

[Copilot]

Pull request overview

This PR improves robustness of JSON request-body decoding when apisix.request_body_json_lib is set to simdjson by retrying with cjson after simdjson decode failures, aiming to keep simdjson as the fast path while preserving previous cjson compatibility.

Changes:

• Add a simdjson→cjson fallback path in apisix.core.request_json.decode() with a warning log on simdjson decode failures.
• Update api7-lua-resty-simdjson dependency to 0.1.2-1.
• Add/adjust tests and update ai-proxy documentation (EN/ZH) to reflect the fallback behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
apisix/core/request_json.lua	Adds simdjson decode wrapper that logs and falls back to cjson decoding on failure.
apisix-master-0.rockspec	Bumps api7-lua-resty-simdjson version to include decoder cleanup after errors.
t/core/request.t	Adds a regression test ensuring fallback to cjson occurs and warning is logged; renumbers subsequent tests.
docs/en/latest/plugins/ai-proxy.md	Documents warning + retry-with-cjson behavior for simdjson mode.
docs/zh/latest/plugins/ai-proxy.md	Same documentation update in Chinese.

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