feat: gas manager for loadtest; add tx-gas-chart

[tclemos]

closes https://github.com/0xPolygon/devtools/issues/444

This PR adds a Gas Manager to the loadtest command and introduces a new tx-gas-chart visualization tool.

Gas Manager features:

• Gas Vault: Budget-based throttling that controls transaction flow per block
• Wave Patterns: Five oscillation patterns (flat, sine, square, triangle, sawtooth) to simulate varying network conditions
• Gas Pricing Strategies: Three strategies (estimated, fixed, dynamic) for flexible gas price simulation

New tx-gas-chart command:

• Generates visual PNG charts analyzing transaction gas prices and limits across block ranges
• Displays four metrics: transaction gas prices, transaction gas limits, block gas limits, and block gas used
• Supports highlighting transactions from/to specific addresses
• Configurable scale (logarithmic or linear) for gas price visualization
• Useful for analyzing gas patterns during load tests or investigating network behavior

Use cases:

• Simulate realistic network congestion patterns during load tests
• Run infinite load tests with controlled gas consumption
• Visualize gas price and usage patterns across blocks
• Stress test networks with oscillating transaction loads

[Copilot]

Pull Request Overview

This PR introduces a gas limiting mechanism for the loadtest command to control transaction flow through configurable gas budgets and oscillation curves. The feature aims to enable running loadtests indefinitely while managing gas consumption patterns.

Key changes:

• Adds a new gaslimiter package implementing a gas vault system and oscillating gas provider
• Refactors loadtest functions to return transaction objects instead of transaction hashes
• Implements gas budget tracking with configurable oscillation curves for dynamic gas limit control

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
cmd/loadtest/gaslimiter/curve.go	Defines base curve interface and configuration for gas oscillation patterns
cmd/loadtest/gaslimiter/curve_sine.go	Implements sinusoidal curve for oscillating gas budgets
cmd/loadtest/gaslimiter/curve_sine_test.go	Tests sine curve implementation with expected values
cmd/loadtest/gaslimiter/gas_vault.go	Implements thread-safe gas budget storage with spend/wait mechanism
cmd/loadtest/gaslimiter/gas_provider.go	Base gas provider that watches for new block headers
cmd/loadtest/gaslimiter/gas_provider_oscillating.go	Oscillating gas provider that adds gas based on curve values per block
cmd/loadtest/gaslimiter/README.md	Documentation for gas limiter components and workflow
cmd/loadtest/loadtest.go	Integrates gas limiter into main loadtest loop and refactors transaction handling
cmd/loadtest/uniswapv3.go	Updates UniswapV3 loadtest to return transaction object instead of hash

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}