Ensure mempool estimates take precedence

[mrfelton]

This pull request introduces several changes in the DataProviderManager.ts, esplora.ts, mempool.ts, and DataProviderManager.test.ts files. The key modifications include the addition of a new MempoolProvider import, changes to the DataProviderManager class constructor, and modifications to the getSortedDataPoints method. Additionally, the EsploraProvider and MempoolProvider class constructors were updated to use a new TIMEOUT constant imported from util. Lastly, a new test case was added to DataProviderManager.test.ts to ensure that providers are sorted correctly.

Changes to DataProviderManager.ts:

• Imported MempoolProvider from ../providers/mempool.
• Updated the DataProviderManager class constructor to provide default values for cacheConfig.
• Modified the getSortedDataPoints method to prioritize mempool-based estimates and made it public.

Changes to esplora.ts and mempool.ts:

• Imported TIMEOUT from ../lib/util and used it as the default value for defaultTimeout in the EsploraProvider and MempoolProvider class constructors [1] [2] [3] [4].
• Updated the example URL in the EsploraProvider class documentation.

Changes to DataProviderManager.test.ts:

• Imported MempoolProvider and EsploraProvider from their respective modules.
• Added a new test case to ensure that providers are sorted correctly.