Remove deprecated nats:Message usages

[aashikam]

Purpose

Fixes: ballerina-platform/ballerina-library#6282

Examples

Checklist

• Linked to an issue
• Updated the changelog
• Added tests
• Updated the spec
• Checked native-image compatibility

[codecov]

Codecov Report

Attention: Patch coverage is 80.55556% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 80.48%. Comparing base (98c2dde) to head (2f3a233).

❗ Current head 2f3a233 differs from pull request most recent head 92de78f. Consider uploading reports for the commit 92de78f to get more accurate results

Files	Patch %	Lines
...lib/nats/basic/consumer/DefaultMessageHandler.java	79.41%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #797      +/-   ##
============================================
- Coverage     80.86%   80.48%   -0.39%     
- Complexity        0      134     +134     
============================================
  Files            30       38       +8     
  Lines          1223     1614     +391     
  Branches        149      254     +105     
============================================
+ Hits            989     1299     +310     
- Misses          168      198      +30     
- Partials         66      117      +51     

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