docs: Update network-fees.mdx and related pages with updated, practical gas management guidance (including post-Azúl considerations).

[hien673]

What changed? Why?

• Gas/fee docs exist but can be more actionable for happy-path + edge cases (e.g., dynamic fees, Flashblocks interaction, estimation best practices).

• Developers often struggle with accurate gasLimit/maxFeePerGas estimation, especially with EIP-1559 + Base-specific behaviors.

• Ties into troubleshooting, node ops, and get-started flows without duplicating content.

• Cross-cutting (useful for apps, agents, contracts) and aligns with cookbook principles.

Notes to reviewers

• Update docs/base-chain/network-information/network-fees.mdx with a new "Best Practices" subsection including code examples.

• Add cross-links from troubleshooting-transactions.mdx, quickstart, and relevant app/agent guides.

• Minor fix: Ensure fee examples use safe patterns (e.g., viem/wagmi estimation, avoid raw keys as noted in issues).

[cb-heimdall]

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