[CLN] Enable full linting - remove continue-on-error from golangci-lint

[tazarov]

Description

Currently, the CI workflow has continue-on-error: true for the golangci-lint step, which means lint failures don't block merges. This is reasonable for initial development but allows technical debt to accumulate.

Current Configuration

File: .github/workflows/ci.yml:46-49

- name: Run golangci-lint
  uses: golangci/golangci-lint-action@v8
  with:
    version: latest
    args: --concurrency=8 --fix
  # Allow lint failures to not block CI while we iteratively improve code quality.
  continue-on-error: true

Problem

• New code can introduce linting issues without anyone noticing
• The --fix flag helps with auto-fixable issues, but not all issues are auto-fixable
• Over time, the number of lint issues will grow
• Makes it harder to enforce code quality standards

Proposed Solution

Phase 1: Assess Current State

1. Run golangci-lint locally and document all current failures
2. Categorize issues by severity and effort to fix
3. Create separate issues for each category

Phase 2: Fix Issues

1. Fix high-severity issues first (bugs, security)
2. Fix medium-severity issues (code quality, maintainability)
3. Address or suppress low-severity issues with justification

Phase 3: Enable Full Linting

1. Remove continue-on-error: true
2. Consider adding linting to pre-commit hooks
3. Document suppression policy (when to use //nolint and why)

Timeline

Target: Before v0.2.0 release (or set a specific date)

Alternative Approach

If fixing all issues at once is too much work:

1. Keep continue-on-error: true for existing code
2. Add a separate lint step for new/changed files only:

   - name: Lint changed files
     run: golangci-lint run --new-from-rev=main
     # This one should NOT have continue-on-error

Acceptance Criteria

• Document all current lint failures
• Create plan to address failures
• Remove continue-on-error OR implement alternative approach
• Add linting policy to CONTRIBUTING.md (when to suppress, how to justify)
• All future PRs must pass linting

Benefits

• Prevents accumulation of technical debt
• Maintains consistent code quality
• Catches potential bugs early
• Makes codebase easier to maintain

Related

• Identified in PR [ENH] Implement ONNX Runtime environment management #15 review
• Part of code quality improvements before v1.0