fix: Refresh proxy collection cache after partition DDL (#49958)

## Summary

Refresh the proxy collection info cache when partition DDL invalidates
partition metadata, so cached `DescribeCollection` reloads
`NumPartitions` from RootCoord after create/drop partition.

Fixes #49782

## Changes

- Stale collection info cache alongside partition cache in
`RemovePartition`.
- Add a regression test that verifies partition invalidation refreshes
cached collection `numPartitions`.

## Test Plan

- `gofumpt -l internal/proxy/meta_cache.go
internal/proxy/meta_cache_test.go`
- `git diff --check`
- `go test -v -count=1 -tags dynamic,test -gcflags="all=-N -l"
-ldflags="-r ${TEST_LIB_WORK_DIR}/cmake_build/lib -r
${TEST_LIB_WORK_DIR}/internal/core/output/lib" ./internal/proxy -run
"TestMetaCache_RemovePartition($|InvalidatesCollectionInfo)" -timeout
300s`

Signed-off-by: sijie-ni-0214 <sijie.ni@zilliz.com>