Add synchronous option to wrap, buffer, bufferTime, debounce, throttle, filtered, and map methods

[jinyus]

Description

Wrapping was synchronous by default which also disabled auto-batching. This PR adds a the ability to customize this.

  test('should NOT autobatch when synchronous=true', () {
    final original = Beacon.writable(10);
    final wrapper = Beacon.writable(0);

    wrapper.wrap(original);
    expect(wrapper.value, 10);

    original.value = 20;
    expect(wrapper.value, 20);

    original.value = 30;
    expect(wrapper.value, 30);
  });

  test('should autobatch when synchronous=false', () async {
    final original = Beacon.writable(10);
    final wrapper = Beacon.writable(0);

    wrapper.wrap(original, synchronous: false);
    expect(wrapper.value, 0);
    await expectLater(wrapper.next(), completion(10));

    original.value = 20;
    original.value = 30;
    original.value = 40;
    original.value = 50;
    expect(wrapper.value, 10); // should not update immediately
    await expectLater(wrapper.next(), completion(50));
  });

Type of Change

• [x] ✨ New feature (non-breaking change which adds functionality)
• [ ] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 Code refactor
• [ ] ✅ Build configuration change
• [ ] 📝 Documentation
• [ ] 🗑️ Chore

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (e5fc7bd) to head (fdfd87b). Report is 47 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #82 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 35 35 Lines 1016 1037 +21 ========================================= + Hits 1016 1037 +21 ``` | [Flag](https://app.codecov.io/gh/jinyus/dart_beacon/pull/82/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jinyus) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/jinyus/dart_beacon/pull/82/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jinyus) | `100.00% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jinyus#carryforward-flags-in-the-pull-request-comment) to find out more.

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