feat: consolidate simplification (#50)

BREAKING CHANGE: The 4.x update consolidates the changes in the 3.x and simplifies a few more steps of the usage experience. It completely removes the ISceneLoader implementations and adds a static MySceneManager class so you don't have to manually control its lifecycle. Refer to the upgrade guide at https://scene-loader.mygamedevtools.com/docs/upgrades/from-3-to-4 for more details.

Author: joaoborks

.github/ISSUE_TEMPLATE/bug_report.yml

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+name: Bug Report
+description: Report a bug or unexpected behavior
+labels: ["bug"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        ## Bug Report
+        Please provide as much detail as possible to help us identify and fix the issue.
+  - type: input
+    id: summary
+    attributes:
+      label: Summary
+      description: A brief summary of the bug
+      placeholder: "Scene transition freezes..."
+    validations:
+      required: true
+  - type: textarea
+    id: steps
+    attributes:
+      label: Steps to Reproduce
+      description: Steps to reproduce the issue
+      placeholder: |
+        1. Load scene A
+        2. Transition to scene B
+        3. Observe the freeze
+    validations:
+      required: true
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected Behavior
+      description: What did you expect to happen?
+    validations:
+      required: true
+  - type: textarea
+    id: actual
+    attributes:
+      label: Actual Behavior
+      description: What actually happened?
+    validations:
+      required: true
+  - type: input
+    id: version
+    attributes:
+      label: Package Version
+      description: The version of the package you are using
+      placeholder: "e.g., 3.1.0"
+    validations:
+      required: true
+  - type: input
+    id: editorversion
+    attributes:
+      label: Unity Editor Version
+      description: The version of the Unity Editor you are using
+      placeholder: "e.g., 6000.0.40f1"
+    validations:
+      required: true
+  - type: textarea
+    id: logs
+    attributes:
+      label: Logs
+      description: Please attach any relevant logs or errors
+      render: shell
+  - type: checkboxes
+    id: terms
+    attributes:
+      label: Acknowledgement
+      options:
+        - label: I have searched the existing issues to avoid duplicates
+          required: true

.github/ISSUE_TEMPLATE/feature_request.yml

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+name: Feature Request
+description: Suggest an idea or enhancement
+labels: ["enhancement"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        ## Feature Request
+        Have a feature idea? Let us know what you'd like to see in My Scene Manager!
+  - type: input
+    id: summary
+    attributes:
+      label: Summary
+      description: A brief summary of the feature
+      placeholder: "Add support for async scene loading with progress callbacks"
+    validations:
+      required: true
+  - type: textarea
+    id: problem
+    attributes:
+      label: Problem or Use Case
+      description: What problem would this feature solve? How would it be useful?
+    validations:
+      required: true
+  - type: textarea
+    id: proposal
+    attributes:
+      label: Proposed Solution
+      description: Describe how you'd like the feature to work
+    validations:
+      required: true
+  - type: checkboxes
+    id: terms
+    attributes:
+      label: Acknowledgement
+      options:
+        - label: I have searched the existing issues to ensure this feature hasn't been requested already
+          required: true