Describe the bug
In create_meta_agent, when assume_constituting_agent_attributes=True or assume_constituting_agent_methods=True, inferred values from constituting agents can overwrite explicitly provided meta_attributes / meta_methods with the same key/name. This makes user-supplied configuration non-authoritative and can change behavior unexpectedly.

Expected behavior
Explicit meta_attributes and meta_methods passed by the caller should take precedence over inferred values. Inference should only fill missing keys/names.

To Reproduce

from mesa import Agent, Model
from mesa.experimental.meta_agents.meta_agent import create_meta_agent

class A(Agent):
    def __init__(self, model):
        super().__init__(model)
        self.custom_attribute = "from_agent"

    def custom_method(self):
        return "from_agent"

model = Model()
a = A(model)

meta = create_meta_agent(
    model,
    "MetaBug",
    [a],
    Agent,
    meta_attributes={"custom_attribute": "explicit"},
    meta_methods={"custom_method": lambda self: "explicit"},
    assume_constituting_agent_attributes=True,
    assume_constituting_agent_methods=True,
)

print(meta.custom_attribute)  # expected: "explicit"
print(meta.custom_method())   # expected: "explicit"

Observed behavior (buggy behavior): explicit values may be replaced by inferred ones from constituent agents.

Additional context

• Area: mesa.experimental.meta_agents.meta_agent.create_meta_agent (add_attributes / add_methods helpers).