Fix minor issues and Add unit tests

[yosuke-wolfssl]

This PR fixes the following issues:

• Add a size check against maximum packet size in DoChannelData and DoChannelExtendedData
• Add a recipient_channel field validation in DoChannelSuccess and DoChannelFailure
• Add an EOF check in SendChannelData and SendChannelExtendedData
• Suppress want_reply for exit-status, exit-signal and window-change to comply with RFC4254.

Also, this adds new unit tests accordingly.

Addressed by f_866, f_867, f_1690 and f_3447.

[Copilot]

Pull request overview

This PR tightens channel message validation and adds internal unit tests for the new channel handling behavior.

Changes:

• Validates recipient channel IDs for CHANNEL_SUCCESS and CHANNEL_FAILURE.
• Adds max packet size and EOF checks for channel data send/receive paths.
• Suppresses replies for RFC-defined no-reply channel requests and adds unit coverage for several new paths.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
wolfssh/internal.h	Exposes additional internal test wrappers under WOLFSSH_TEST_INTERNAL.
src/internal.c	Updates channel request/data handling and adds internal wrapper implementations.
tests/unit.c	Adds unit tests for channel success/failure, data overflow, and EOF send behavior.

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[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #982

Scan targets checked: wolfssh-bugs, wolfssh-src

No new issues found in the changed files. ✅