[Feature request] AgentCoreToolSearchPlugin: add tool_filters support to restrict tools resolved from AgentCore Gateway

**Is your feature request related to a problem? Please describe.**
When using AgentCoreToolSearchPlugin with AgentCore Gateway, there is currently no way to restrict which tools are surfaced to the agent. The plugin performs semantic search over the full set of tools registered in the Gateway, which can include dozens of tools. Without filtering, the semantic search may surface unintended tools, which increases noise, wastes tokens, and can cause the agent to invoke tools it should not have access to.

**Describe the solution you'd like**
AgentCoreToolSearchPlugin should support a tool_filters parameter, mirroring the tool_filters parameter already available on Strands' MCPClient:
```python
# Current Strands MCPClient — already supports filtering
MCPClient(
...,
tool_filters={"allowed": ["tool-1", "tool-2"]}
)

# Desired — AgentCoreToolSearchPlugin parity
AgentCoreToolSearchPlugin(
...,
tool_filters={"allowed": ["tool-1", "tool-2"]}
)
```
Ideally, the filter should be applied before (or at query time during) the semantic search, so that only candidate tools matching the allowlist are considered. If not possible, it can be done after query result I guess inside the `x_amz_bedrock_agentcore_search` tool call.

**Describe alternatives you've considered**
Post-filtering after semantic search with the post tool call hook and discarding results that don't match the allowlist. This works but should be natively supported by the plugin.

**Additional context**
N/A

AgentCoreToolSearchPlugin とその x_amz_bedrock_agentcore_search ツール呼び出しから始め、次に Strands MCPClient が tool_filters をどのように処理するかを比較します。許可されたツールのフィルターをサポートし、セマンティック検索で許可されたツールだけが考慮されるようにします。また、AgentCoreToolSearchPlugin がサンプルの tool_filters パラメーターを受け入れ、許可されていない結果を除外することを確認します。

索引モデルが issue の本文から書いたものです。