fix(webdav): handle weak and quoted gzip ETags

[joshtrichards]

Summary

Better Android WebDAV ETag parsing with the desktop client's behavior.

The redundant lowercase response-header lookups were also removed because both underlying response APIs perform case-insensitive header-name matching.

Previously, parseEtag():

• Removed -gzip only before removing surrounding quotes.
• Did not remove the weak ETag prefix (W/).
• Therefore failed to normalize values such as W/"abc-gzip": the -gzip suffix was hidden behind the closing quote, and W/ was retained.

This change normalizes ETags in the following order:

1. Remove the weak validator prefix (W/).
2. Remove surrounding double quotes.
3. Remove a trailing -gzip suffix.

Examples:

Raw ETag	Before	After
W/"abc-gzip"	W/"abc-gzip"	abc
"abc-gzip"	abc-gzip	abc
"abc-gzip-value"	abc-gzip-value	abc-gzip-value
abc-gzip-gzip	abc-gzip	abc-gzip

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI

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SpotBugs

Category	Base	New
Bad practice	31	31
Correctness	28	28
Dodgy code	13	13
Internationalization	6	6
Malicious code vulnerability	26	26
Multithreaded correctness	7	7
Performance	3	3
Security	3	3
Total	117	117