feat: improve nodata and dtype handling

[hrodmn]

This PR ensures that the correct dtype and nodata are maintained in the array's encoding and metadata attributes. If not provided by the user, dtype and nodata are inferred from the assets in a sample STAC item and are validated at runtime when each file is opened.

This also fixes a bug in the mosaic operations where nodata pixels were auto-filled with zeros by the MosaicMethod.

[github-actions]

Benchmark Comparison

Test	Baseline (ms)	PR (ms)	Change
test_band_access_pattern[multi_band]	1312.7	825.1	-37.1%
test_band_access_pattern[single_band]	1216.9	774.8	-36.3%
test_full_compute	634.0	399.0	-37.1%
test_mosaic_method[first]	633.0	385.2	-39.1%
test_mosaic_method[median]	667.8	406.1	-39.2%
test_native_crs_resolution	11637.0	6653.0	-42.8%
test_open_overhead	282.5	160.1	-43.3%
test_reproject_workers[1]	2546.5	1587.1	-37.7%
test_reproject_workers[4]	1322.6	860.5	-34.9%
test_time_step_parallelism[dask_time_1]	1339.2	830.0	-38.0%
test_time_step_parallelism[no_dask]	931.6	581.1	-37.6%