fix(rocketmq): log warning when FLAG or DELAY header is not numeric

[daguimu]

Describe what this PR does / why we need it

RocketMQMessageConverterSupport#getAndWrapMessage parses the MQ_FLAG and DELAY_TIME_LEVEL Spring Messaging headers into int via Integer.parseInt. The previous implementation wrapped both parses in try { ... } catch (Exception ignored) {}, so any malformed header (e.g. a String value injected via a SpEL expression, a typo, or a non-numeric class) was silently absorbed and the producer fell back to flag=0 and delayLevel=0 with no exception, no log line, and no signal to the caller.

The most user-visible consequence is on the delayed-delivery path: a misconfigured DELAY_TIME_LEVEL (e.g. "abc" from a SpEL that returned a String instead of an int) turns a delayed message into an immediate send and the application has no way of knowing.

Does this pull request fix one issue?

NONE

Describe how you did it

• Added a class-level SLF4J logger to RocketMQMessageConverterSupport.
• Replaced catch (Exception ignored) {} with catch (Exception e) { log.warn(...) }, including both header names (MQ_FLAG, DELAY_TIME_LEVEL) and their raw values in the warning so the misconfiguration is diagnosable.
• Lifted the DELAY_TIME_LEVEL header lookup out of the try block so the catch clause can reference the raw value; both lookups are side-effect-free, so this is a no-op on the happy path. Parse order is unchanged (delayLevel first, then flag).
• Kept the runtime fallback (flag=0, delayLevel=0) and the broad catch (Exception) to avoid any behaviour change for existing producers — only observability is added.

Describe how to verify it

mvn -pl spring-cloud-alibaba-starters/spring-cloud-starter-stream-rocketmq -am test (all 13 module tests pass locally, including 3 new ones).

New tests in RocketMQMessageConverterSupportTest:

• nonNumericDelayTimeLevelHeaderFallsBackToZero — sets DELAY = "not-a-number", asserts rkmqMsg.getDelayTimeLevel() == 0.
• nonNumericFlagHeaderFallsBackToZero — sets MQ_FLAG = "not-a-number", asserts rkmqMsg.getFlag() == 0.
• invalidNumericHeaderDoesNotPropagateException — sets both headers to non-numeric values and asserts no exception escapes convertMessage2MQ.

These tests pass both before and after the fix; their role is regression lock-in for the silent-fallback semantics. The warning itself is verified manually by running with --logging.level.com.alibaba.cloud.stream.binder.rocketmq=WARN and sending a message with a malformed DELAY header.

Special notes for reviews

• Behaviour-preserving change: identical outputs for every previously valid header value; identical fallback outputs for every previously-swallowed bad value; new log.warn is the only externally visible difference.
• The new tests cannot mutation-verify the log.warn because the fix does not change the message-conversion output. I left them in as regression guards rather than introducing a new log-capture testing pattern (e.g. OutputCaptureExtension) that the module doesn't currently use elsewhere.
• The try block's parse order is unchanged — delayLevel parses first, then flag. This matters in the unlikely case where one is numeric and the other isn't, and I wanted to keep that observable behaviour identical.