fix: don't error on static assignment if rebalancing should take place

[bmckerry]

To horizontally scale the US transactions cluster, we're trying to give topicctl specific assignments for topics in the cluster via static placement (see docs).
Currently, running a topicctl apply --rebalance on a topic with static replica assignments is getting this error:

[2025-05-01 15:31:40]  INFO Here are the number of partitions per broker now, during the migration, and after:
---------+------------+------------+-------------
  BROKER |    CURR    |    MAX     |  PROPOSED
         | PARTITIONS | PARTITIONS | PARTITIONS
---------+------------+------------+-------------
  0      | 128        | 128        |  32 (-96)
  1      | 128        | 128        |  43 (-85)
  2      | 128        | 128        |  32 (-96)
  3      | 0          |  32 (+32)  |  32 (+32)
  4      | 0          |  42 (+42)  |  42 (+42)
  5      | 0          |  43 (+43)  |  43 (+43)
  6      | 0          |  32 (+32)  |  32 (+32)
  7      | 0          |  43 (+43)  |  43 (+43)
  8      | 0          |  42 (+42)  |  42 (+42)
  9      | 0          |  43 (+43)  |  43 (+43)
---------+------------+------------+-------------
[2025-05-01 15:31:40]  INFO They will be applied in batches of 1 partitions each, with a throttle of 512000000000000 bytes/sec (512000000 MB/sec)
[2025-05-01 15:31:40]  INFO Skipping update because dryRun is set to true
[2025-05-01 15:31:40]  INFO Checking leaders...
[2025-05-01 15:31:40]  INFO Running rebalance...
[2025-05-01 15:31:40] ERROR Error detected while creating or updating a topic
[2025-05-01 15:31:40] ERROR starting assignments on topic ingest-transactions-2 do not satisfy placement config

If I'm understanding the code correctly, the current implementation of Rebalance() using PlacementStrategyStatic makes it so that a rebalance will never happen, as it throws an error if the current replica assignments don't match the static assignments being specified.
I'm not sure what the purpose of this is, so this PR changes the case where current placement != desired static placement to just log something instead of erroring. More details below.

[bmckerry]

When applying a new topic, if EvaluateAssignments returns false, topicctl knows it needs to adjust the partition placement of the new topic to match the desired placement strategy: https://github.com/getsentry/topicctl/blob/master/pkg/apply/apply.go#L831

When rebalancing a topic (which is what this frequency.go file is used for), if EvaluateAssignments returns false, topicctl considers that to be an error. I've updated it so that if we're using static placement, topicctl doesn't error out here when rebalancing.

[evanh]

Looks good!