feat(gnovm): add extensible linting framework with AVL001 and GLOBAL001 rules

[MikaelVallenet]

fix #4421 & fix #1042

Summary

This PR adds an extensible linting framework to gno lint. You can now write pluggable rules, choose different
output formats, and suppress warnings with //nolint comments.

What's New

New Lint Package (gnovm/pkg/lint/)

Core stuff:

• Issue - represents a single lint finding (severity, location, message)
• Severity - three levels: info, warning, error
• Rule interface - implement this to create your own lint rules
• RuleContext - gives rules access to the file, source code, and parent nodes
• Registry - handles rule registration (rules self-register via init())
• Config - controls mode and which rules to disable
• NolintParser - reads //nolint comments to suppress specific issues

Reporters (how output gets formatted):

• TextReporter - human-friendly output, sorted by file/line, with a summary at the end
• JSONReporter - machine-readable JSON array for tooling integration
• DirectReporter - prints issues immediately as they're found (used by gno test)

Built-in rules:

• AVL001 - warns when you iterate an entire AVL tree without bounds (tree.Iterate("", "", ...))
• GLOBAL001 - warns about exported package-level variables (like var Counter int)

CLI Changes (gnovm/cmd/gno/lint.go)

New flags:

• --mode - choose between default, strict, or warn-only
• --format - output as text or json
• --list-rules - shows all available rules and exits
• --disable-rules - skip specific rules (e.g., --disable-rules=AVL001,GLOBAL001)

Output format changed:
Before

  file.gno:10:5: some message (code=someCode)

After

  file.gno:10:5: warning: some message (AVL001)

Docs

• Added docs/resources/gno-lint.md with usage examples, rule descriptions, and a guide for writing new rules

Tests

• Unit tests for everything in gnovm/pkg/lint/
• Integration tests (txtar format) covering AVL001, GLOBAL001, nolint directives, and mode flags

Breaking Changes

Output format - The lint output now includes severity and uses a different format (see above)

Exit codes - Now depend on the mode:

Mode	Exits with 1 when...
default	there are errors
strict	there are any issues (warnings become errors)
warn-only	never (errors become warnings)

[Gno2D2]

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Changes to 'docs' folder must be reviewed/authored by at least one devrel and one tech-staff

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[codecov]

Codecov Report

❌ Patch coverage is 84.93724% with 72 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
gnovm/cmd/gno/lint.go	63.01%	22 Missing and 5 partials ⚠️
gnovm/cmd/gno/common.go	60.60%	23 Missing and 3 partials ⚠️
gnovm/pkg/lint/rules/avl001.go	83.92%	5 Missing and 4 partials ⚠️
gnovm/pkg/lint/registry.go	91.66%	2 Missing ⚠️
gnovm/pkg/lint/reporters/direct.go	86.66%	2 Missing ⚠️
gnovm/pkg/lint/reporters/json.go	92.85%	2 Missing ⚠️
gnovm/pkg/lint/rules/global001.go	95.00%	1 Missing and 1 partial ⚠️
gnovm/pkg/lint/severity.go	92.30%	1 Missing and 1 partial ⚠️

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