Fix(huaweidrive): Replace fullwidth encoding with percent-encoding (%XX)

Fix: Replace fullwidth encoding with percent-encoding (%XX)

I've pushed a fix in commit ace14fb85 that resolves the 19 FsEncoding + FsPutFiles CI failures.

Root Cause

The previous scheme substituted restricted characters with their Unicode fullwidth equivalents (e.g., ? → ？ U+FF1F, . → ． U+FF0E). This worked on most Huawei Drive deployments, but the CI account's API applies NFKC normalization before filename validation, which converts fullwidth ASCII variants straight back to their ASCII originals:

This triggered HTTP 400 errorCode 21004002 on every retry.

Fix

Replace the opt.Enc-based fullwidth scheme with a custom percent-encoding scheme (hwEncodeFilename / hwDecodeFilename):

• ? → %3F, . (whole-name) → %2E, < → %3C, \x00 → %00, etc.
• % itself → %25 (to keep encoding invertible)
• Leading space/dot/tilde and trailing space/dot also percent-encoded
• Invalid UTF-8 bytes encoded one byte at a time (\xfe → %FE)

The % character is not on the Huawei API blacklist, and pure ASCII %XX sequences are completely stable under NFKC normalization.

The encoding config option has been removed — the backend now manages filename encoding internally.

Verification

Local integration test results (all 19 FsEncoding subtests + FsPutFiles):

--- PASS: TestIntegration/FsMkdir/FsEncoding/control_chars
--- PASS: TestIntegration/FsMkdir/FsEncoding/dot
--- PASS: TestIntegration/FsMkdir/FsEncoding/dot_dot
--- PASS: TestIntegration/FsMkdir/FsEncoding/punctuation
--- PASS: TestIntegration/FsMkdir/FsEncoding/leading_space
--- PASS: TestIntegration/FsMkdir/FsEncoding/leading_tilde
--- PASS: TestIntegration/FsMkdir/FsEncoding/leading_CR/LF/HT/VT
--- PASS: TestIntegration/FsMkdir/FsEncoding/leading_dot
--- PASS: TestIntegration/FsMkdir/FsEncoding/trailing_space/CR/LF/HT/VT/dot
--- PASS: TestIntegration/FsMkdir/FsEncoding/invalid_UTF-8
--- PASS: TestIntegration/FsMkdir/FsEncoding/URL_encoding
--- PASS: TestIntegration/FsMkdir/FsPutFiles  (including "hello? sausage" path)

Start with the Huawei Drive backend's hwEncodeFilename and hwDecodeFilename entry points, then review the FsEncoding and FsPutFiles integration tests named in the issue. Verify percent-encoding remains invertible across the listed filename cases and that the removed encoding option is no longer needed. Done means all 19 FsEncoding subtests and FsPutFiles pass against Huawei Drive.