chore: convert bug report template to GitHub form (#4015)

Converts the bug report issue template from markdown to GitHub's YAML
form format. This provides a more structured experience for users
filing bug reports with:

- Required version and platform fields
- Separate sections for code, expected behavior, and actual behavior
- Better input validation
- Improved readability for maintainers

Closes #3213

Author: njg7194

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,65 @@
+name: "Bug report 🐛"
+description: Create a report to help us improve
+labels: ["C-bug"]
+body:
+  - type: input
+    id: version
+    attributes:
+      label: Version
+      description: List the version(s) of `hyper`, and any relevant hyper dependency (such as `h2` if this is related to HTTP/2).
+      placeholder: "hyper 1.0.0, h2 0.4.0"
+    validations:
+      required: true
+
+  - type: input
+    id: platform
+    attributes:
+      label: Platform
+      description: The output of `uname -a` (UNIX), or version and 32 or 64-bit (Windows)
+      placeholder: "Linux 5.15.0 x86_64 / Windows 11 64-bit"
+    validations:
+      required: true
+
+  - type: textarea
+    id: summary
+    attributes:
+      label: Summary
+      description: A short summary of the bug
+      placeholder: "Brief description of what went wrong"
+    validations:
+      required: true
+
+  - type: textarea
+    id: code
+    attributes:
+      label: Code Sample
+      description: Code sample that causes the bug (if applicable)
+      render: rust
+      placeholder: |
+        use hyper::...;
+
+        fn main() {
+            // code that reproduces the bug
+        }
+
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected Behavior
+      description: What you expected to happen
+    validations:
+      required: true
+
+  - type: textarea
+    id: actual
+    attributes:
+      label: Actual Behavior
+      description: What actually happened instead
+    validations:
+      required: true
+
+  - type: textarea
+    id: additional
+    attributes:
+      label: Additional Context
+      description: Any other context about the problem (stack traces, related issues, etc.)