first test for data inventory

[LOCEANlloydizard]

Following the removal of the test_data/README.md file in this PR, and the discussion in #1562 (particularly here), this PR introduces a centralized YAML inventory for echopype test data bundles. The inventory is validated in CI against the Pooch bundle registry (conftest.py) to ensure that all test data bundles are documented and remain synchronized. The inventory is also integrated into the RTD documentation.

The documented_checksum field is introduced as the basis for future validation that bundle metadata has been reviewed whenever a GitHub release asset changes => in progress

Ref #1565

[leewujung]

@LOCEANlloydizard : just noticed a small thing. Also do you intend to add the checksum field in this PR? Sorry not sure if this PR is finished or not, but I think it's a great idea!

[LOCEANlloydizard]

notes from #1703

ek80_heading.zip:
documented_checksum: 141b9a482af22483097de6f928db4d7b0494d4f7a153f88cffd24c070e11fadb
instrument: ES80
description: ES80 raw data containing NMEA HDT messages used to test heading parsing when heading is unavailable from MRU datagrams.
source: Collected during a sphere calibration of a 38 kHz ES80 on a fishing vessel (name deliberately omitted)
contributor: gavinmacaulay
references: []
notes: Used by test_convert_ek80::test_parse_NMEA_heading
files: {D20260613-T230914.raw}

[LOCEANlloydizard]

notes from #1714

azfp_single_frequency.zip:
documented_checksum: 71c7c095522208d0a4e773cf4dd082c93c8f27bb75ef729f4307586d6565dc5c
instrument: AZFP
description: ULS5 AZFP raw data and XML configuration for an instrument configured with only one active 125 kHz channel.
source: Provided by ZHANGGU in echopype issue #1256.
contributor: ZHANGGU
references:
- #421
- #1256
- #1714
notes: Used by test_convert_azfp::test_convert_azfp_01a_single_frequency
files: {14021116.XML, 14021117.01A}