The default resolution doesn't allow aggregating

[dolegi]

Title: Resolution mismatch causes cryptic error when aggregating - needs better handling or error message

Description:

When a TimeFrame has a very small default resolution (microseconds) and you try to aggregate to a much larger period (days), it fails with a cryptic Polars type conversion error instead of handling the case gracefully or providing a helpful error message.

Expected Behavior:

Either:

• Automatically handle the resolution mismatch, or
• Provide a clear error message explaining that the resolution needs to be adjusted before aggregating to the target period

Actual Behavior:

Fails with: polars.exceptions.InvalidOperationError: conversion from 'i128' to 'u32' failed in column 'scalar' for 1 out of 1 values: [86400000000]

Reproduction:

import time_stream as ts
from datetime import datetime, timedelta
import polars as pl

# Create sample data
dates = [datetime(2023, 1, 1) + timedelta(days=i) for i in range(10)]
temperatures = [20.5, 21.0, 19.1, 26.0, 24.2, 26.6, 28.4, 30.9, 31.0, 29.1]
precipitation = [0.0, 0.0, 5.1, 10.2, 2.0, 0.2, 0.0, 3.0, 1.6, 0.0]

df = pl.DataFrame({
    "time": dates,
    "temperature": temperatures,
    "precipitation": precipitation
})

tf = ts.TimeFrame(df=df, time_name="time")
print(tf)
# Shows: Resolution: PT0.000001S (microseconds)

# Attempt to aggregate to daily resolution
tf.aggregate('P1D', 'mean', 'precipitation')  # Fails with conversion error

Environment:

• Python 3.12
• time_stream (version from traceback paths)
• polars (version from traceback paths)