feat(api): allow configurable CORS policy

[TheRealSibasishBehera]

Fixes #3481 kind:feat

Enforces CORS configuration rules and adds middleware handling.

• Introduces CORS flags (--rpc.cors-enabled, --rpc.cors-allowed-origins, --rpc.cors-allowed-methods, --rpc.cors-allowed-headers)

• Requires --rpc.cors-enabled=true to use any CORS-related flags

• Using --rpc.skip-auth allows all CORS settings (equivalent to * wildcard)

• Provides default values when partial configuration is given

• Fully overwrites (does not extend) settings when all configurations are provided, giving users complete control

[TheRealSibasishBehera]

@walldiss Could you please review this PR? Let me know if anything needs further changes. Many thanks 🙏

[TheRealSibasishBehera]

@walldiss Thanks for looking into the middleware libraries. I’ve added tests for the middleware function—let me know if you think it needs any improvement or additional tests.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 79.54545% with 27 lines in your changes missing coverage. Please review.

Project coverage is 35.54%. Comparing base (2469e7a) to head (2585c13). Report is 516 commits behind head on main.

Files with missing lines	Patch %	Lines
nodebuilder/rpc/flags.go	77.77%	6 Missing and 12 partials :warning:
nodebuilder/rpc/constructors.go	0.00%	6 Missing :warning:
cmd/util.go	0.00%	3 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4266      +/-   ##
==========================================
- Coverage   44.83%   35.54%   -9.29%     
==========================================
  Files         265      323      +58     
  Lines       14620    25195   +10575     
==========================================
+ Hits         6555     8956    +2401     
- Misses       7313    15270    +7957     
- Partials      752      969     +217     

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