[Concept]: feat: introducing lazy chain loading (#644)

Chains can now be loaded lazily instead of eager, this means chains will
only be loaded when it is being used.

Hidden under the feature toggle `CLD_LAZY_BLOCKCHAINS` , off by default.

Basically this solves a bunch of issues
- avoid loading all the chains in the network config file even they are
not used (increases loading time)
- failures on loading certain chains that are not used will now not
failed the changeset
- users having to always specify chain overrides in input yaml in order
to avoid loading all the chains (this can be tricky if the chain
overrides is a long list of chains too)
- basically deprecate the `ChainsOverrides` feature, simplifying the
code

Author: graham-chainlink

.changeset/empty-words-tickle.md

@@ -0,0 +1,7 @@
+---
+"chainlink-deployments-framework": minor
+---
+
+feat(chain): introduce lazy chain loading
+
+feature toggle under CLD_LAZY_BLOCKCHAINS environment variable to enable lazy loading of chains.

chain/blockchain.go

@@ -24,6 +24,10 @@ var _ BlockChain = sui.Chain{}
 var _ BlockChain = ton.Chain{}
 var _ BlockChain = tron.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 {
@@ -35,6 +39,22 @@ 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 {