refactor: integration of base signer/observer structure

[ws4charlie]

Description

The PR integrated Signer and Observer structures into existing EVM/BTC Signer and Observer structures.

Closes: 2022
Closes: 2126

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Include instructions and any relevant details so others can reproduce.

• Tested CCTX in localnet
• Tested in development environment
• Go unit tests
• Go integration tests
• Tested via GitHub Actions

Checklist:

• I have added unit tests that prove my fix feature works

[gitguardian]

⚠️ GitGuardian has uncovered 1 secret following the scan of your pull request.

Please consider investigating the findings and remediating the incidents. Failure to do so may lead to compromising the associated services or software components.

🔎 Detected hardcoded secret in your pull request

GitGuardian id	GitGuardian status	Secret	Commit	Filename
11759679	Triggered	Generic High Entropy Secret	5edd452	cmd/zetae2e/local/accounts.go	View secret

🛠 Guidelines to remediate hardcoded secrets

1. Understand the implications of revoking this secret by investigating where it is used in your code.
2. Replace and store your secret safely. Learn here the best practices.
3. Revoke and rotate this secret.
4. If possible, rewrite git history. Rewriting git history is not a trivial act. You might completely break other contributing developers' workflow and you risk accidentally deleting legitimate data.

To avoid such incidents in the future consider

• following these best practices for managing and storing secrets including API keys and other credentials
• install secret detection on pre-commit to catch secret before it leaves your machine and ease remediation.

---

^{🦉 GitGuardian detects secrets in your source code to help developers and security teams secure the modern development process. You are seeing this because you or someone else with access to this repository has authorized GitGuardian to scan your pull request.}

[github-actions]

!!!WARNING!!!
nosec detected in the following files: zetaclient/chains/bitcoin/signer/signer.go, zetaclient/chains/evm/signer/signer.go

Be very careful about using #nosec in code. It can be a quick way to suppress security warnings and move forward with development, it should be employed with caution. Suppressing warnings with #nosec can hide potentially serious vulnerabilities. Only use #nosec when you're absolutely certain that the security issue is either a false positive or has been mitigated in another way.

Only suppress a single rule (or a specific set of rules) within a section of code, while continuing to scan for other problems. To do this, you can list the rule(s) to be suppressed within the #nosec annotation, e.g: /* #nosec G401 */ or //#nosec G201 G202 G203
Broad #nosec annotations should be avoided, as they can hide other vulnerabilities. The CI will block you from merging this PR until you remove #nosec annotations that do not target specific rules.

Pay extra attention to the way #nosec is being used in the files listed above.

[ws4charlie]

use separate PR to integrate base observer

[codecov]

Codecov Report

Attention: Patch coverage is 46.42857% with 30 lines in your changes missing coverage. Please review.

Project coverage is 68.70%. Comparing base (5e3c3ba) to head (7faa962).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2355      +/-   ##
===========================================
- Coverage    68.72%   68.70%   -0.03%     
===========================================
  Files          302      302              
  Lines        19168    19160       -8     
===========================================
- Hits         13174    13163      -11     
- Misses        5347     5350       +3     
  Partials       647      647              

Files	Coverage Δ
zetaclient/chains/evm/signer/signer.go	53.09% <80.00%> (-0.88%)	⬇️
zetaclient/tss/tss_signer.go	9.81% <0.00%> (ø)
zetaclient/chains/bitcoin/signer/signer.go	18.21% <23.07%> (-1.14%)	⬇️