Update minimum base fee to 5,000,000 wei

[niran]

Summary

• Update minimum base fee from 2,000,000 to 5,000,000 wei (0.005 gwei) on both Base Mainnet and Base Sepolia
• Update cost example in network fees docs
• Add changelog entries for the 5M minimum base fee on both networks

Also captures missing Feb 10 Sepolia parity changes:

• Update Sepolia EIP-1559 Denominator from 50 to 125 (matching Mainnet)
• Add changelog entries for Sepolia Denominator increase and 2M minimum base fee

Context

• Contract deployment PR: feat(mainnet,sepolia): add task to update min base fee to 5M wei contract-deployments#595
• Previous docs PRs: docs: update minimum base fee to 2,000,000 wei #1100 (2M), Update minimum base fee docs for 1,000,000 wei #894 (1M), Increase minimum base fee to 500,000 wei #740 (500K)

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1