fix(middleware): restore previous response writer in BodyDump

[rajpreetcodes]

What this PR does

Fixes #3173: middleware.BodyDump installs a wrapper bodyDumpResponseWriter on Context via c.SetResponse, but never restores the previous response writer before returning.

Because Echo.serveHTTP executes HTTPErrorHandler after the middleware chain unwinds, any error formatted by the error handler writes into the still-installed wrapper response writer. At that point, the underlying dump buffer (resBuf) has already been handed back to bodyDumpBufferPool via defer bodyDumpBufferPool.Put(resBuf). This creates a data race on bytes.Buffer under concurrent traffic and risks corrupting pooled request/response buffers.

Solution

1. Capture origResponse := c.Response() before setting the wrapper.
2. Defer restoring c.SetResponse(origResponse) so the previous response writer is restored whenever the middleware returns (normally, on error, or on panic).
3. Because deferred calls execute LIFO, c.SetResponse(origResponse) runs before bodyDumpBufferPool.Put(resBuf), guaranteeing that c.Response() is restored before the buffer is returned to the pool and before HTTPErrorHandler writes.

Changes

• middleware/body_dump.go: save and defer restoring previous response writer.
• middleware/body_dump_test.go:
  • TestBodyDump_RestoreResponse: asserts that c.Response() is restored to its original value after BodyDump completes.
  • TestBodyDump_ErrorHandlerRace: exercises concurrent error handling under BodyDump with multiple goroutines.

Verification

• go test ./...: all packages pass (github.com/labstack/echo/v5, echotest, middleware).
• go test -v -run TestBodyDump_RestoreResponse ./middleware: confirmed failure on pre-fix code (expected: *echo.Response, actual: *middleware.bodyDumpResponseWriter), passes cleanly with fix.
• Code formatted with gofmt -s.

[rajpreetcodes]

@vishr This PR implements the fix proposed in #3173 by deferring c.SetResponse(origResponse), restoring the original response writer before BodyDump returns and before the global HTTPErrorHandler writes. Unit and concurrent data race test suites are included.