Add minimal user-defined functions implementation

[rkalis]

• Add top-level user-defined function syntax
  • Functions can return a single value or nothing
• Add import syntax
• Imports are resolved and flattened into a single AST before compiler traversals
• Used functions are defined at the top of a contract, their function
  bodies are compiled with a separate GenerateTargetTraversal + optimisations
• Update builtin function compilation to self-document their bytecode
• Update docs & release notes

This version does NOT YET support:

• Multiple return values / tuples
• Proper SDK debugging integration
• Nested / multiple returns in a function
• Advanced optimisations
• Global constants
• Cross-file pragma resolutions

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Project	Deployment	Actions	Updated (UTC)
cashscript	Ready	Preview, Comment	Jun 26, 2026 2:05pm

[codecov]

Codecov Report

❌ Patch coverage is 96.04520% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.31%. Comparing base (53f286b) to head (7edbfc4).

Files with missing lines	Patch %	Lines
packages/cashc/src/Errors.ts	85.00%	3 Missing ⚠️
...kages/cashc/src/print/OutputSourceCodeTraversal.ts	82.35%	3 Missing ⚠️
packages/cashc/src/ast/AST.ts	91.30%	2 Missing ⚠️
.../cashc/src/semantic/EnsureFinalRequireTraversal.ts	92.85%	2 Missing ⚠️
packages/cashc/src/ast/AstBuilder.ts	97.14%	1 Missing ⚠️
packages/cashc/src/ast/AstTraversal.ts	90.00%	1 Missing ⚠️
...es/cashc/src/generation/GenerateTargetTraversal.ts	96.87%	1 Missing ⚠️
packages/utils/src/types.ts	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next     #413      +/-   ##
==========================================
+ Coverage   85.69%   86.31%   +0.61%     
==========================================
  Files          51       55       +4     
  Lines        4041     4318     +277     
  Branches      757      805      +48     
==========================================
+ Hits         3463     3727     +264     
- Misses        453      465      +12     
- Partials      125      126       +1     

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