Support attachments/embeds via io/fs.FS #115

Job	Run time
Dependency review	11s
Go vulnerabilities check	20s
Test with Codecov coverage (ubuntu-latest / 1.23)	1m 7s
REUSE Compliance Check	17s
golangci-lint (1.23)	38s
Test with SonarQube review (ubuntu-latest / 1.23)	2m 15s
Test (macos-latest / 1.19)	44s
Test (macos-latest / 1.20)	43s
Test (macos-latest / 1.21)	40s
Test (macos-latest / 1.22)	20s
Test (macos-latest / 1.23)	38s
Test (ubuntu-latest / 1.19)	29s
Test (ubuntu-latest / 1.20)	1m 1s
Test (ubuntu-latest / 1.21)	27s
Test (ubuntu-latest / 1.22)	39s
Test (ubuntu-latest / 1.23)	40s
Test (windows-latest / 1.19)	1m 15s
Test (windows-latest / 1.20)	1m 40s
Test (windows-latest / 1.21)	1m 44s
Test (windows-latest / 1.22)	1m 27s
Test (windows-latest / 1.23)	1m 56s
Test on FreeBSD 13.4'	2m 33s
Test on FreeBSD 14.0	2m 10s
Test on FreeBSD 14.1	2m 35s
	26m 29s

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