docs: add changelog for recent changes (#12)

Author: naingaunglwin-dev

CHANGELOG.md

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+# ChangeLog
+
+## v1.1.0 - 2025-12-09
+### Added
+- Implemented `__toString()` method for the `Result` class, allowing instances to be converted to strings (e.g. `"$result"` now returns the calculated value). (PR #1)
+- Added new `stop()` method to the timer, supporting stopping: (PR #2)
+    - a specific timer by ID
+    - **or** the **most recently started timer** when no ID is provided.
+- Added new `watch()` static method to replace `run()` for executing and timing callbacks. (PR #4)
+- Added new timer utility methods `isStarted()`, `isStopped()`, and `getActiveTimers()` in `TimeTracker` to inspect active and completed timers. (PR #7)
+- Added new timer utility methods `lap()`, `getLaps()`, `pause()`, `resume()`, and `inspect()` in `TimeTracker`. (PR #9)
+
+### Changed
+- Replaced `ramsey/uuid` with native PHP functions (`bin2hex(random_bytes(16))`) for generating random IDs. (PR #3)
+- Removed the `ramsey/uuid` dependency as it is no longer required. (PR #3)
+- Replaced `STATUS_*` string constants with a dedicated `TimerStatus` enum. (PR #5)
+
+### Fixed
+- Prevent duplicate `stop()` calls in `watch()` by adding an `isStopped()` check in the `finally` block. (RP #8)
+
+### Deprecated
+- Marked `end()` as deprecated. It still works for backward compatibility but will be removed in a future major release. (PR #2)
+- Marked `run()` as deprecated. It still works for backward compatibility but will be removed in a future major release. (PR #4)