Use schedule class instead of lambdas

[araffin]

Description

See Stable-Baselines-Team/stable-baselines3-contrib#294

Motivation and Context

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist:

• I've read the CONTRIBUTION guide (required)
• I have updated the changelog accordingly (required).
• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
• I have reformatted the code using make format (required)
• I have checked the codestyle using make check-codestyle and make lint (required)
• I have ensured make pytest and make type both pass. (required)

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[Copilot]

Pull Request Overview

This PR replaces lambda-based schedules with dedicated schedule classes for improved portability, bumps the version and dependencies to 2.6.1a1, and updates the changelog.

• Bump sb3_contrib dependency and version to 2.6.1a1
• Introduce SimpleLinearSchedule and replace linear_schedule/constant_fn with class-based schedules
• Update imports in exp_manager.py and reflect changes in CHANGELOG.md

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
setup.py	Bumped sb3_contrib requirement to >=2.6.1a1
rl_zoo3/version.txt	Updated package version to 2.6.1a1
rl_zoo3/utils.py	Added SimpleLinearSchedule class and alias function
rl_zoo3/exp_manager.py	Switched from linear_schedule/constant_fn to class schedules
CHANGELOG.md	Documented breaking changes and schedule refactor

Comments suppressed due to low confidence (2)

rl_zoo3/utils.py:295

• Add unit tests for SimpleLinearSchedule (e.g., verifying output for given progress_remaining values and the __repr__ string) to ensure correct behavior and prevent regressions.

class SimpleLinearSchedule:

CHANGELOG.md:5

• The changelog refers to linear_fn, but the actual function is named linear_schedule. Update the entry to match the correct function name to avoid confusion.

- `linear_fn` now returns a `SimpleLinearSchedule` object for better portability

[Copilot]

Pull Request Overview

This PR refactors the scheduling functionality by replacing lambda-based schedules with a dedicated schedule class, SimpleLinearSchedule, and updates corresponding tests and dependencies.

• Introduced a new SimpleLinearSchedule class in rl_zoo3/utils.py
• Updated tests in tests/test_wrappers.py to validate the new schedule class
• Updated dependency versions and version.txt accordingly

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/test_wrappers.py	Added tests for new schedule functionality and updated related imports
setup.py	Bumped the sb3_contrib dependency version
rl_zoo3/version.txt	Updated package version
rl_zoo3/utils.py	Replaced lambda-based linear_schedule with SimpleLinearSchedule class
rl_zoo3/exp_manager.py	Updated schedule and constant functions usage to use the new classes
CHANGELOG.md	Updated release notes to reflect breaking changes and new features

Comments suppressed due to low confidence (1)

rl_zoo3/utils.py:310

• [nitpick] Consider adding tests to verify the output of repr for SimpleLinearSchedule to ensure future maintainability.

def __repr__(self) -> str: