add issue and pr templates

[dpo]

Strongly inspired by the SciML templates.

What feature report was addressed?

Added GitHub Issue and Pull Request templates to standardize reporting and contribution workflows across JuliaSmoothOptimizers repositories.

Checklist

• Appropriate tests were added
• The new feature was added in a way that does not break public API
• New documentation related to the new feature was added
• The new code follows the contributor guidelines.

Please also check one of the following:

• All of the new code was written by a human without the assistance of an AI
• Some of the new code was written by an AI, and the AI-generated code was reviewed and edited by a human to ensure quality and correctness
• Some of the new code was written by an AI, but the AI-generated code was NOT reviewed and edited by a human to ensure quality and correctness.

Additional context

• Added PR templates for bugfixes, new features, performance changes, and documentation fixes.
• Added issue templates for bug reports, feature requests, feature regressions, and new algorithm suggestions.
• Fixed all checklist items to use - [ ] (with a space) so they render as interactive GitHub checkboxes.
• Fixed grammar and spelling in issue template MRE descriptions (proper capitalization, "Stack Overflow", etc.).
• Corrected performance PR template header to reference performance issues/regressions rather than bugs.
• Fixed grammar in new algorithm issue template ("what you want us to add").

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Pull request overview

Adds GitHub Issue and Pull Request templates to standardize reporting and contribution workflows, inspired by SciML’s community templates.

Changes:

• Added PR templates for bugfixes, new features, performance changes, and documentation fixes.
• Added issue templates for bug reports, feature requests, feature regressions, and new algorithm suggestions.
• Included structured prompts for MREs, environment capture, benchmarks, and contributor checklists.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
.github/PULL_REQUEST_TEMPLATE/performance.md	New PR template focusing on benchmarks + performance-related checklist.
.github/PULL_REQUEST_TEMPLATE/new_feature.md	New PR template for feature work with tests/docs checklist and AI attestation.
.github/PULL_REQUEST_TEMPLATE/documentation_fix.md	New PR template for documentation-only changes with public-API reminder.
.github/PULL_REQUEST_TEMPLATE/bugfix.md	New PR template emphasizing MRE-to-test and downstream impact checks.
.github/ISSUE_TEMPLATE/new_algorithm.md	New issue template for proposing algorithms and references.
.github/ISSUE_TEMPLATE/feature_request.md	New issue template for feature requests including alternatives.
.github/ISSUE_TEMPLATE/feature_regression.md	New issue template for regressions with working/non-working environment capture.
.github/ISSUE_TEMPLATE/bug_report.md	New issue template for bug reports including MRE + environment details.

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[dpo]

@MaxenceGollier How does this look?