feat: introducing lazy chain loading

Chains are loaded lazily instead of eager, this means chains will only be loaded when it is being used, this means users are not forced to provide any secrets for chains if they are not used upfront and avoid loading huge amount of chains that are never used.

This change also means we can deprecate `ChainOverrides` feature as we no longer have to tell CLD what chains to load.

This lazy loading is hidden under the feature flag CLD_LAZY_BLOCKCHAINS

However there is a migration needed to take advantage of lazy laoding as i want to maintain backwards compatibility.

eg
```
	// Previously: env.BlockChains.EVMChains()
	// Preferred: env.Chains().EVMChains()
```

Author: graham-chainlink

.changeset/empty-words-tickle.md

@@ -0,0 +1,13 @@
+---
+"chainlink-deployments-framework": minor
+---
+
+feat(chain): introduce lazy chain loading
+
+Feature toggle under CLD_LAZY_BLOCKCHAINS environment variable to enable lazy loading of chains.
+Migration guide:
+
+- Previously: env.BlockChains.EVMChains()
+- Preferred: env.Chains().EVMChains()
+
+By using the newer Chains() method, you can now access newer features such as loading the chains lazily, which is useful for large environments.

chain/blockchain.go

@@ -26,6 +26,10 @@ var _ BlockChain = ton.Chain{}
 var _ BlockChain = tron.Chain{}
 var _ BlockChain = canton.Chain{}
 
+// Compile-time checks that both BlockChains and LazyBlockChains implement BlockChainCollection
+var _ BlockChainCollection = BlockChains{}
+var _ BlockChainCollection = (*LazyBlockChains)(nil)
+
 // BlockChain is an interface that represents a chain.
 // A chain can be an EVM chain, Solana chain Aptos chain or others.
 type BlockChain interface {
@@ -37,6 +41,22 @@ type BlockChain interface {
 	Family() string
 }
 
+// BlockChainCollection defines the common interface for accessing blockchain instances.
+// Both BlockChains and LazyBlockChains implement this interface.
+type BlockChainCollection interface {
+	GetBySelector(selector uint64) (BlockChain, error)
+	Exists(selector uint64) bool
+	ExistsN(selectors ...uint64) bool
+	All() iter.Seq2[uint64, BlockChain]
+	EVMChains() map[uint64]evm.Chain
+	SolanaChains() map[uint64]solana.Chain
+	AptosChains() map[uint64]aptos.Chain
+	SuiChains() map[uint64]sui.Chain
+	TonChains() map[uint64]ton.Chain
+	TronChains() map[uint64]tron.Chain
+	ListChainSelectors(options ...ChainSelectorsOption) []uint64
+}
+
 // BlockChains represents a collection of chains.
 // It provides querying capabilities for different types of chains.
 type BlockChains struct {