lib: use MTYPEs for northbound in several places

[mjstapp]

Stop using MTYPE_TMP in several places; use NB-specific MTYPEs for visibility.

[greptile-apps]

Greptile Overview

Greptile Summary

This PR replaces several MTYPE_TMP allocations in the northbound core and northbound CLI/VTY integration with NB-specific MTYPEs to improve memory-accounting visibility. Specifically, northbound config-change/callback allocations now use MTYPE_NB_CONFIG, transaction allocations use a new MTYPE_NB_TRANS, and the VTY pending command buffer uses a new exported MTYPE_NB_CMDS (declared in northbound_cli.h and freed in vty.c).

I did not find any allocation/free mismatches or build-breaking issues in the changed hunks; the new MTYPE declarations/definitions are consistent with the existing DECLARE_MTYPE/DEFINE_MTYPE patterns and the cross-file free in vty.c now matches the allocator’s MTYPE.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk.
• Changes are limited to memory-type tagging for existing allocations/frees; the modified sites keep correct allocation/free pairing and the only cross-file MTYPE is properly declared/defined via existing macros.
• No files require special attention

Important Files Changed

Filename	Overview
lib/northbound.c	Replaces several northbound allocations/frees from MTYPE_TMP to NB-specific MTYPEs (NB_CONFIG/NB_TRANS) and adds NB_TRANS memtype; no allocation/free mismatches found.
lib/northbound_cli.c	Introduces exported MTYPE_NB_CMDS and switches pending_cmds_buf allocation/realloc/free to it; matches free sites in vty.c; no issues found.
lib/northbound_cli.h	Adds DECLARE_MTYPE(NB_CMDS) so vty.c can use MTYPE_NB_CMDS; header/API change is consistent with existing memory.h patterns.
lib/vty.c	Switches pending_cmds_buf free from MTYPE_TMP to MTYPE_NB_CMDS to match northbound_cli.c allocation; include visibility relies on northbound_cli.h; no functional issues found.

Sequence Diagram

sequenceDiagram
    participant CLI as northbound_cli
    participant VTY as vty
    participant NB as northbound

    CLI->>VTY: Append pending commands
    Note over CLI,VTY: pending_cmds_buf allocated/realloc'd with MTYPE_NB_CMDS
    VTY->>VTY: vty_close() cleanup
    VTY->>VTY: XFREE(MTYPE_NB_CMDS, pending_cmds_buf)
    NB->>NB: Create config change
    Note over NB: XCALLOC/XFREE with MTYPE_NB_CONFIG
    NB->>NB: Create transaction
    Note over NB: XCALLOC/XFREE with MTYPE_NB_TRANS

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[donaldsharp]

LGTM, I'll get in once CI finishes