this allows external packages, like the GoSNMPServer,  to use gosnmp to handle encrypted sessions.

Signed-off-by: Liam Kelly <liam@commdevices.com>

Make InitPacket and InitSecurityKeys public

- Ensure idempotent and thread-safe Close behavior.
- Close connection for both TCP and UDP without protocol checks.
- Use atomic operations for safer concurrent handling.
- Await "done" signal before complete closure, ensuring clean shutdown.

Fixes:
- Address potential issue where the connection might not be closed in certain conditions

Enhances:
- Configurable TrapListener.CloseTimeout with a default of 3 seconds.

Signed-off-by: Tim Rots <tim.rots@protonmail.ch>

Signed-off-by: Liam Kelly <liam@commdevices.com>

Allow RequestID to be shrunk if possible

* Initial net-snmp validation testing

running go test with -tags=netsnmp will cause the test to use packets generated by net-snmp as expected values. This requires libsnmpd to be installed and cgo. Adding -rec=true to this will also record the expected packets as files under /testdata. These files can then be used without cgo in normally testing.

An additional pcap generating feature was also added, when -pcap $DIR is added to go test that directory will be filled with the expected and generated packets as pcaps. This allows for debugging using wireshark's parsers.

* Counter32 support added to '*Gosnmp.Set' and validated
* Add support Set support and validate most PDU types. Also add Uinteger32 parse support.

Fixes: #453

---------

Signed-off-by: Liam Kelly <liam@commdevices.com>

Add a 60s fuzzing test to the CI test pipeline.

Signed-off-by: SuperQ <superq@gmail.com>

* Allow global password cache to be turned off

The global password cache is undesirable for higher security applications as a user's cache entry would remain even if the calling package deleted the corresponding `UsmSecurityParameters`.

Disabling this mechanism comes with a significant performance hit, as seen by running the added benchmark tests with the build tag `gosnmp_nopwdcache`.

There is also a middle ground approach, where the calling package can reset the cache by turning it off then on again. This should clear any stale entries and still allow the cache to be leveraged.

Signed-off-by: Liam Kelly <liam@commdevices.com>

Bumps [github.com/google/go-cmp](https://github.com/google/go-cmp) from 0.5.9 to 0.6.0.
- [Release notes](https://github.com/google/go-cmp/releases)
- [Commits](google/go-cmp@v0.5.9...v0.6.0)

---
updated-dependencies:
- dependency-name: github.com/google/go-cmp
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>