goto-instrument: add early output file validation

[tautschnig]

Validate output file presence before expensive analysis operations to prevent wasted computation when command is malformed.

Fixes: #2593

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.00%. Comparing base (b191cc1) to head (53fc818).

Files with missing lines	Patch %	Lines
.../goto-instrument/goto_instrument_parse_options.cpp	66.66%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8784      +/-   ##
===========================================
- Coverage    80.01%   80.00%   -0.01%     
===========================================
  Files         1700     1700              
  Lines       188345   188354       +9     
  Branches        73       73              
===========================================
+ Hits        150696   150699       +3     
- Misses       37649    37655       +6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Copilot]

Pull request overview

Adds an early validation step in goto-instrument to ensure an output file is provided for operations that mutate the model, avoiding wasted work when the command line is malformed.

Changes:

• Introduces a pre-check for missing output filename before running expensive analysis.
• Whitelists “read-only” operations that don’t require an output file.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.