Allocate channelName dynamically to shrink WOLFSSH struct by ~4KB

[aidangarske]

Description

Converts the WOLFSSH.channelName field from a fixed 4096-byte inline array to a
dynamically-allocated buffer sized to the actual subsystem/exec name, cutting wolfSSH_new()'s per-connection allocation by 4096 bytes with no change to public
API behavior. It also short-circuits the allocation when the name is unchanged,
so the non-blocking SFTP/SCP handshake retry loops no longer churn malloc/free
on every poll.

Measured wolfSSH_new() allocation (−4096 B in every config):

• 64-bit --enable-all: 11568 -> 7472 B
• 64-bit minimal: 8400 -> 4304 B
• 32-bit minimal: 7648 -> ~3556 B

Adds test_wolfSSH_SetChannelType covering the full branch set (NULL/zero/oversize
name, store+NUL-terminate, unchanged-name no-op, replace/free-previous, EXEC
fallthrough, unknown-type and server-side EXEC rejection).

Fixes concerns in: ZD 21984

[Copilot]

Pull request overview

This PR reduces per-connection memory usage by changing WOLFSSH.channelName from a fixed-size inline buffer to a dynamically allocated buffer sized to the actual subsystem/exec name, and adds API tests to cover the updated channel-type/name behavior.

Changes:

• Replace WOLFSSH.channelName[WOLFSSH_MAX_CHN_NAMESZ] with byte* channelName and allocate/free it dynamically.
• Update wolfSSH_SetChannelType() to avoid realloc churn when the channel name is unchanged and to NUL-terminate stored names.
• Add test_wolfSSH_SetChannelType to cover the new/updated branches and edge cases.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
wolfssh/internal.h	Shrinks WOLFSSH by making channelName a pointer instead of a 4KB inline array.
src/ssh.c	Implements dynamic allocation + “unchanged name” fast-path in wolfSSH_SetChannelType().
src/internal.c	Frees channelName in SshResourceFree() and adjusts debug logging in SendChannelRequest().
tests/api.c	Adds a new API test to validate wolfSSH_SetChannelType() behavior across edge cases.

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