chore: Fix amount rendering for balance/amounts

This fixes the rendering for Balance, CryptoAmount, and FiatAmount, to
print out the BigDecimals as a float.

They were erroneously printing the `amount` as an integer, which removes
the precision unnecessarily.

lib/coinbase/balance.rb

@@ -43,7 +43,7 @@ def initialize(amount:, asset:, asset_id: nil)
     # Returns a string representation of the Balance.
     # @return [String] a string representation of the Balance
     def to_s
-      "Coinbase::Balance{amount: '#{amount.to_i}', asset_id: '#{asset_id}'}"
+      Coinbase.pretty_print_object(self.class, amount: amount.to_s('F'), asset_id: asset_id)
     end
 
     # Same as to_s.

lib/coinbase/crypto_amount.rb

@@ -50,7 +50,7 @@ def to_atomic_amount
     # Returns a string representation of the CryptoAmount.
     # @return [String] a string representation of the CryptoAmount
     def to_s
-      Coinbase.pretty_print_object(self.class, amount: amount.to_i, asset_id: asset_id)
+      Coinbase.pretty_print_object(self.class, amount: amount.to_s('F'), asset_id: asset_id)
     end
 
     # Same as to_s.

lib/coinbase/fiat_amount.rb

@@ -28,7 +28,7 @@ def initialize(amount:, currency:)
     # Returns a string representation of the FiatAmount.
     # @return [String] a string representation of the FiatAmount
     def to_s
-      Coinbase.pretty_print_object(self.class, amount: amount.to_i, currency: currency)
+      Coinbase.pretty_print_object(self.class, amount: amount.to_s('F'), currency: currency)
     end
 
     # Same as to_s.

spec/unit/coinbase/balance_spec.rb

@@ -138,11 +138,11 @@
   describe '#inspect' do
     subject(:balance) { described_class.new(amount: amount, asset: asset) }
 
-    let(:amount) { BigDecimal('123.0') }
+    let(:amount) { BigDecimal('123.456') }
     let(:asset) { Coinbase::Asset.from_model(eth_asset) }
 
     it 'includes balance details' do
-      expect(balance.inspect).to include('123', 'eth')
+      expect(balance.inspect).to include('123.456', 'eth')
     end
 
     it 'returns the same value as to_s' do

spec/unit/coinbase/crypto_amount_spec.rb

@@ -149,11 +149,11 @@
   describe '#inspect' do
     subject(:crypto_amount) { described_class.new(amount: amount, asset: asset) }
 
-    let(:amount) { BigDecimal('123.0') }
+    let(:amount) { BigDecimal('123.456') }
     let(:asset) { Coinbase::Asset.from_model(eth_asset) }
 
     it 'includes crypto_amount details' do
-      expect(crypto_amount.inspect).to include('123', 'eth')
+      expect(crypto_amount.inspect).to include('123.456', 'eth')
     end
 
     it 'returns the same value as to_s' do

spec/unit/coinbase/fiat_amount_spec.rb

@@ -57,10 +57,10 @@
   describe '#inspect' do
     subject(:fiat_amount) { described_class.new(amount: amount, currency: currency) }
 
-    let(:amount) { BigDecimal('123.0') }
+    let(:amount) { BigDecimal('123.456') }
 
     it 'includes fiat_amount details' do
-      expect(fiat_amount.inspect).to include('123', 'usd')
+      expect(fiat_amount.inspect).to include('123.456', 'usd')
     end
 
     it 'returns the same value as to_s' do