Added documentation to MiniExcelConverter and fixed warnings in tests and benchmarks projects

[michelebastione]

As per the title, this PR adds the long overdue documentation to the MiniExcelConverter utility class and makes a few small changes that finally fix all warnings in the tests and benchmark projects (mostly nullable reference types checks).

Summary by CodeRabbit

• Bug Fixes
  • Improved asynchronous cleanup during picture processing.
  • Enhanced stream handling for CSV↔XLSX conversions, including safer disposal of temporary resources.
  • Updated converter docs to clarify that stream-based conversion methods do not close the provided streams.
• Tests
  • Strengthened CSV and OpenXML tests for nullable values and optional results to reduce brittle assumptions.
  • Adjusted CSV test casting to fail fast on incompatible runtime types.
• Chores
  • Enabled the benchmark license acceptance setting.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: a86c472c-f7ef-492f-b1d6-d9c2a93c59a3

📥 Commits

Reviewing files that changed from the base of the PR and between e187dff and c35969f.

📒 Files selected for processing (2)

• src/MiniExcel.Core/Helpers/FileHelper.cs
• src/MiniExcel/MiniExcelConverter.cs

🚧 Files skipped from review as they are similar to previous changes (1)

• src/MiniExcel/MiniExcelConverter.cs

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📝 Walkthrough

Walkthrough

The changes update CSV/XLSX conversion stream disposal, OpenXML reader disposal, benchmark license configuration, nullable assumptions in CSV and OpenXML tests, and formatting in a file-opening helper.

Changes

Converter and async disposal

Layer / File(s)	Summary
Converter stream lifecycle src/MiniExcel/MiniExcelConverter.cs	File-path overloads conditionally use synchronous or asynchronous stream disposal; stream overloads preserve caller-owned streams and retain CSV/XLSX conversion behavior.
Picture reader async disposal src/MiniExcel.OpenXml/Picture/OpenXmlPictureImplement.cs	AddPictureAsync now disposes the OpenXML reader with await using.

Benchmark configuration and nullable test models

Layer / File(s)	Summary
Nullable test expectations tests/MiniExcel.Csv.Tests/Main/*, tests/MiniExcel.OpenXml.Tests/...	Tests use nullable model members and extracted results, explicit dictionary casts, and null-safe mapping assertions.
Benchmark license setting benchmarks/MiniExcel.Benchmarks/MiniExcel.Benchmarks.csproj	The benchmarks project enables AcceptNPOIOSMFLicense.

Helper formatting

Layer / File(s)	Summary
File helper formatting src/MiniExcel.Core/Helpers/FileHelper.cs	OpenSharedRead is reformatted without changing its file-opening behavior.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main changes: MiniExcelConverter documentation and warning fixes in tests and benchmarks.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/MiniExcel/MiniExcelConverter.cs`:
- Around line 26-34: Register each acquired stream for disposal immediately
before opening the next stream: in src/MiniExcel/MiniExcelConverter.cs lines
26-34, dispose csvStream before constructing xlsxStream; in
src/MiniExcel/MiniExcelConverter.cs lines 78-86, dispose xlsxStream before
constructing csvStream. Preserve the existing SYNC_ONLY and asynchronous
disposal behavior.
- Around line 92-94: Update the XML summary for the affected conversion method
to describe XLSX-to-CSV conversion: it reads XLSX data from the input stream and
writes CSV data to the output stream asynchronously.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c8cca028-bc61-4208-b876-a3f6578c1760

📥 Commits

Reviewing files that changed from the base of the PR and between 3266e8b and e187dff.

📒 Files selected for processing (8)

• benchmarks/MiniExcel.Benchmarks/MiniExcel.Benchmarks.csproj
• src/MiniExcel.OpenXml/Picture/OpenXmlPictureImplement.cs
• src/MiniExcel/MiniExcelConverter.cs
• tests/MiniExcel.Csv.Tests/Main/MiniExcelCsvTests.cs
• tests/MiniExcel.Csv.Tests/Main/Models.cs
• tests/MiniExcel.OpenXml.Tests/FluentMapping/MiniExcelMappingTests.cs
• tests/MiniExcel.OpenXml.Tests/Templates/InputValueExtractorTests.cs
• tests/MiniExcel.OpenXml.Tests/Templates/Models.cs