freat: add date_to_unix_ts/3 function to the rule engine

[kjellwinblad]

Fixes https://emqx.atlassian.net/browse/EMQX-9245

Summary

🤖 Generated by Copilot at 8435571

Add a new rule engine function date_to_unix_ts/3 to convert date strings to unix timestamps and a test case for it in emqx_rule_funcs_SUITE.erl.

PR Checklist

Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:

• Added tests for the changes
• Changed lines covered in coverage report
• Change log has been added to changes/{ce,ee}/(feat|perf|fix)-<PR-id>.en.md files
• For internal contributor: there is a jira ticket to track this change
• If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
• Schema changes are backward compatible

[coveralls]

Pull Request Test Coverage Report for Build 4719918024

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 431 unchanged lines in 43 files lost coverage.
• Overall coverage increased (+0.08%) to 81.236%

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Files with Coverage Reduction	New Missed Lines	%
apps/emqx_authn/src/enhanced_authn/emqx_enhanced_authn_scram_mnesia.erl	1	86.57%
apps/emqx_modules/src/emqx_delayed.erl	1	94.78%
apps/emqx_modules/src/emqx_modules_schema.erl	1	95.24%
apps/emqx_slow_subs/src/emqx_slow_subs_schema.erl	1	83.33%
apps/emqx/src/emqx_channel.erl	1	87.64%
apps/emqx/src/emqx_sys_mon.erl	1	90.63%
apps/emqx/src/emqx_cm.erl	2	91.89%
apps/emqx/src/emqx_limiter/src/emqx_limiter_bucket_ref.erl	2	88.24%
lib-ee/emqx_ee_bridge/src/emqx_ee_bridge.erl	2	95.74%
apps/emqx_resource/src/schema/emqx_resource_schema.erl	3	95.56%

Totals
Change from base Build 4687261328:	0.08%
Covered Lines:	25518
Relevant Lines:	31412

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💛 - Coveralls

[thalesmg]

I think this is called only once for all tests. I tried locally with nanosecond and printing the value, it's always the same.

To achieve the desired generation of values, I think one way is to do:

Suggested change

	erlang:system_time(second),
	?LAZY(erlang:system_time(second)),

Not sure if the most correct way to produce values, but does produce different values.

Also, note that the generation is very fast: it produces several values in a second. So, even with ?LAZY, this will basically always return the same value.

Perhaps we could instead define a range of epoch values? Like

Suggested change

	erlang:system_time(second),
	range(0, 4000000000),

[kjellwinblad]

Thanks, I think this problem existed in the other test cases in the same function as well. Will try to fix them too.

[kjellwinblad]

@thalesmg thanks for spotting this. I have updated the test case in the latest commit.