Match RFC 2047 encoding token case-insensitively in decodeWord

[alhudz]

Repro: Content-Disposition: attachment; filename="=?utf-8?b?ZXZpbC5leGU=?=", a valid RFC 2047 encoded-word that uses the lower-case b marker.
Expected: the filename decodes to evil.exe, matching the upper-case =?utf-8?B?...?= form.
Actual: MimeUtils.decodeWord throws UnsupportedEncodingException, so ParameterParser keeps the raw value =?utf-8?b?ZXZpbC5leGU=?=. Lower-case q behaves the same way against the Q marker.
Cause: the charset token is lower-cased before use, but the encoding token is compared case-sensitively with encoding.equals("B") / equals("Q"). RFC 2047 section 2 defines the encoding as case-independent (b == B, q == Q).
Fix: compare the encoding token with equalsIgnoreCase, so b/q decode identically to B/Q. Two regression tests cover the lower-case base64 and quoted-printable markers; both fail before the change.

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[Copilot]

Pull request overview

This PR fixes RFC 2047 “encoded-word” decoding in MimeUtils.decodeWord by treating the encoding token (B/Q) case-insensitively, ensuring lower-case markers (b/q) decode correctly (e.g., for Content-Disposition filenames).

Changes:

• Update decodeWord to compare the encoding token using equalsIgnoreCase for both Base64 (B) and quoted-printable (Q).
• Add regression tests covering lower-case b and q encoding markers.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
commons-fileupload2-core/src/main/java/org/apache/commons/fileupload2/core/MimeUtils.java	Makes RFC 2047 encoding token matching case-insensitive in decodeWord.
commons-fileupload2-core/src/test/java/org/apache/commons/fileupload2/core/MimeUtilityTestCase.java	Adds tests to verify lower-case b/q markers decode correctly.

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[garydgregory]

@alhudz Merged 🚀 Thank you, please port to 1.x.