feat(gnovm): align Gno constant handling with Go specifications

[omarsy]

Related Issues:
#2628

This PR aims to align Gno's constant handling with the Go specification regarding constant expressions (see Go Specification on Constants).

1. Primitive Type Requirement

   • Should Work:

     const t = 1

   • Should Return an Error:

     const t = []string{"1"}

     Error:

     (const (slice[("1" string)] []string)) (value of type []string) is not constant
     

2. Function Calls Disallowed
   Only built-in functions should be allowed.

   • Should Work:

     const t = len("s")

   • Should Return an Error:

     func v() string {
         return ""
     }
     const t = v()

     Error:

     v<VPBlock(3,0)>() (value of type string) is not constant
     

3. Constant Operands Requirement
   Constant expressions may contain only constant operands and are evaluated at compile time.

   • Should Work:

     const t = 1
     const v = t

   • Should Raise an Error:

     t := 1
     const v = t

     Error:

     t (variable of type int) is not constant
     

4. Type Assertion Forbidden

   • This code:

     var i interface{} = 1
     const t, ok = i.(int)

   • Should Raise This Error:

     i.(int) (comma, ok expression of type int) is not constant
     

5. Index Expression Forbidden

   • This code:

     var i = []string{}
     const t, ok = i[0]

   • Should Return This Error:

     i[0] (variable of type string) is not constant
     

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.88%. Comparing base (5503cca) to head (78ec19f).
Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2828      +/-   ##
==========================================
+ Coverage   60.83%   60.88%   +0.05%     
==========================================
  Files         563      563              
  Lines       75193    75235      +42     
==========================================
+ Hits        45743    45809      +66     
+ Misses      26076    26060      -16     
+ Partials     3374     3366       -8     

Flag	Coverage Δ
contribs/gnodev	61.46% <ø> (ø)
contribs/gnofaucet	14.46% <ø> (ø)
misc/genstd	80.54% <ø> (ø)
misc/logos	20.23% <ø> (ø)
tm2	62.08% <ø> (+0.19%)	⬆️

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